Effects on reproduction of estrous cycle variations, rectal temperatures and liveweights in mated Brahman cross heifers

Estrous cycle variations and the association of rectal temperature with reproductive measurements and liveweight were examined in 25-month-old 1/2 and 3/4 Brahman heifers (n = 88). The mean cycle length was longer in the 1/2 Brahmari (24.3 days) than in the 3 4 Brahman heifers (21.3 days) due to the length of estrus-metestrus, but the overall difference was not statistically significant. Cycle length was not influenced by cycle number or liveweight. Cycles were classified into 6 types: normal, short, long, anovulatory and those involving embryonic mortality and prolonged diestrus. Only 33.6% of 1/2 Brahman cycles and 36.1% of 3/4 Brahman cycles were of normal duration (18 to 24 days), and 13.3% of 1/2 Brahman and 11.6% of 3/4 Brahman cycles were classified as embryonic mortality cycles. On an individual animal basis, 25.0% and 31.8% of 3 4 Brahman heifers, respectively, had cycles in which embryonic mortality was suspected. Heifers that became pregnant were significantly (P < 0.01) heavier throughout mating and had significantly (P < 0.05) lower mean rectal temperatures. Heifers in which embryonic mortality had occurred were lighter and had significantly (P < 0.01) higher rectal temperatures than heifers in which embryonic mortality had not occurred. Correlations between rectal temperature and ambient temperature were nonsignificant after eliminating the effect of genotype, but rectal temperature was significantly (P < 0.01) negatively correlated with liveweight.

Synchronization of estrus and fertility in zebu beef heifers treated with three estrus synchronization protocols

The effects on estrus and fertility of 3 estrus synchronization protocols were studied in Brahman beef heifers. In Treatment 1 (PGF protocol; n=234), heifers received 7.5 mg, i.m. prostianol on Day 0 and were inseminated after observed estrus until Day 5. Treatment 2 (10-d NOR protocol; n = 220) consisted of norgestomet (NOR; 3 mg, s.c. implant and 3 mg, i.m.) and estradiol valerate (5 mg, i.m.) treatment on Day -10, NOR implant removal and 400 IU, i.m. PMSG on Day 0, and AI after observed estrus through to Day 5. Treatment 3 (14-d NOR+PGF protocol; n = 168) constituted a NOR implant (3 mg, sc) on Day -14, NOR implant removal on Day 0, PGF on Day 16, and AI after observed estrus through to Day 21. All heifers were examined for return to estrus at the next cycle and inseminated after observed estrus. The heifers were then exposed to bulls for at least 21 d. During the period of estrus observation (5 d) after treatment, those heifers treated with the PGF protocol had a lower (P<0.01) rate of estrual response (58%) than heifers treated with the 10-d NOR (87%) or 14-d NOR+PGF (88%) protocol. Heifers treated with the 10-d NOR protocol displayed estrus earlier and had a closer synchrony of estrus than heifers treated with either the PGF or the 14-d NOR+PGF protocol. Heifers treated with the 14-d NOR+PGF protocol had higher (P<0.05) conception and calving rates (51 and 46%) to AI at the induced estrus than heifers treated with the PGF (45 and 27%) or the 10-d NOR (38 and 33%) protocol. Calving rate to 2 rounds of AI was greater (P<0.05) for heifers treated with the 14-d NOR-PGF (50%) protocol than heifers treated with the 10-d NOR (38%) but not the PGF (43%) protocol. Breeding season calving rates were similar among the 3 protocols. The results show that the 14-d NOR+PGF estrus synchronization protocol induced a high incidence of estrus with comparatively high fertility in Brahman heifers.

A comparison of dissected follicle numbers and follicle counts on the ovarian surface for the evaluation of ovarian follicular populations in Bos indicus cows

Ovaries (n = 140) from 70 mixed-age multiparous, lactating Brahman cross (3/4 - 7/8 Bos indicus) cows were used to examine the hypothesis that counts of follicles visible on the surface of the ovaries of Bos indicus cows and their classification into diameter size classes, are closely correlated with numbers of follicles in those size classes found by complete dissection of the ovary. Immediately after ovariectomy, mean diameters (long and short axes averaged) of all follicles > or = 2 mm visible on the surface of each ovary were measured. All follicles > or = 2 mm were dissected from the ovaries, excess stroma removed and follicle diameters measured under a stereomicroscope using an ocular graticule. For each ovary, follicles were classified in either small (< 4 mm), medium (4-8 mm) or large (> 8 mm) categories based on either diameters of surface or dissected follicles. Data for numbers of surface and dissected follicles (mean +/- SE) in small, medium, large categories and total follicle numbers, respectively, were 24.4 +/- 1.6 vs. 28.0 +/- 1.9, 1.6 +/- +0.2 vs. 11.6 +/- 1.0, 0.5 +/- 0.1 vs. 0.7 +/- 0.1 and 26.4 +/- 1.6 vs. 40.4 +/- 2.5. Correlation coefficients (r) for counts of surface and dissected follicles in small, medium, large and total follicle numbers were 0.76, 0.40, 0.69 and 0.79, respectively. Medium size follicles presented only a small translucent area on the surface of the ovary, leading to an underestimate of numbers when categorised by surface evaluation. Counts of follicles visible on the surface of the ovaries of Bos indicus cows and their classification into size classes based on estimated diameter, are closely correlated with numbers of follicles in those size classes found at dissection of the ovary for small (< 4 mm), large (> 8 mm) and total follicles but not for medium sized (4-8 mm) follicles.

Prepartum supplementation effects on growth and fertility in Bos indicus-cross cows

Summary. Three experiments were conducted in the dry tropics of north Australia using Bos indicus-cross cows. Cows in mid–late pregnancy were either unsupplemented during the late dry season or offered ad libitum (2 kg/day) molasses with 7.4% urea (w/w) (M8U) or cottonseed meal (1 kg/day) for up to 54 days commencing 2 months before the start of the calving season. Supplementation reduced weight loss in experiments 1 and 2 (P<0.05), but had no significant effect on weight or body condition in experiment 3. Supplementation had no effect on subsequent calf growth or cow lactation yields. Following early wet season rains in experiment 1, 9 and 49% of cows were ovulating 40 and 80 days post-partum, respectively, with no effect of supplementation. In experiment 2, 10 and 100% of cows had ovulated by 60 and 200 days post-partum, respectively. At any time between 80 and 180 days post-partum, supplemented cows were more likely to be cycling (P<0.05), independent of supplementation effects on weight or body condition. The average post-partum interval to oestrus was 30 days less in cows supplemented for 42 days (P = 0.08). In experiment 3, pregnancy rates in 1/2 and 3/4 Brahmans supplemented with M8U for 54 days (MU54) or whose calves were weaned at 2–3 months of age (WEAN) were 14% higher in the latter 2 months of mating than in cows supplemented for less than 40 days. Good seasonal conditions resulted in high pregnancy rates in all mature 5/8 Brahmans; when not weaned early, their average calving to conception interval (CCI) was 54 days (s.e. = 8.5 days). Pregnancy rates of first-lactation 5/8 Brahmans (average CCI of 125 days) supplemented for 39 days or less and weaned when calves averaged 6 months of age were 14–32% lower between 2 and 9 months post-partum than in contemporaries in the MU54 or WEAN treatment groups. It was concluded that dry-season supplementation of mid- to late-pregnant Bos indicus-cross cows with an energy concentrate for 42–54 days (‘spike’ feeding) may reduce post-partum anoestrus intervals via a mechanism which is not dependent on the effects on weight or body condition.

Changes in ovarian function and gonadotropin secretion preceding the onset of nutritionally induced anestrus in Bos indicus heifers

The aim of this study was to monitor endocrine and ovarian changes immediately preceding the onset of nutritionally induced anestrus. Daily blood samples were obtained from 14 postpubertal heifers for one estrous cycle (initial estrous cycle). Subsequently, heifers designated "restricted" were given a limited diet (n = 9), and daily blood samples were obtained for approximately 21 days preceding onset of anestrus (anovulatory cycle). Controls were allowed ad libitum dietary intake (n = 5), and daily blood samples were collected for a complete estrous cycle during a time period that coincided with that preceding onset of anestrus in restricted heifers. Plasma samples were assayed for LH, FSH, progesterone, and estradiol-17 beta. The ovaries of all heifers were examined daily using transrectal ultrasonography from the initial until the final or anovulatory estrous cycles to determine changes in growth of follicles and corpora lutea. Anestrus was defined as failure of ovulation of the dominant follicle following luteolysis. When anovulatory and initial estrous cycles in restricted heifers were compared, mean concentrations of LH were lower (p < 0.01), and diameters of dominant follicles were smaller (p < 0.01); mean concentrations of estradiol-17 beta were also lower in the three days following luteolysis (p = 0.06), but concentrations of FSH appeared to be higher (p = 0.003); maximum diameters of corpora lutea were smaller (p < 0.001), but duration of luteal phases and concentrations of progesterone preceding luteolysis were similar (p > 0.10). In controls, no differences were found between estrous cycles for any of these variables. It is concluded that failure of ovulation, following reduced dietary intake, resulted from insufficient circulating LH to stimulate maturation of the ovulatory follicle.

Reducing post-partum anoestrous interval in first-calf Bos indicus crossbred beef heifers. III. Effect of nutrition on responses to weaning and associated variation in metabolic hormone levels

Interactions between effects of undernutrition and weaning on the duration of post-partum anoestrus and associated variation in milk yield, suckling behaviour, and metabolic hormone levels in Droughtmaster [Bos indicus x Bos taurus (518, 3/8)] first-calf cows were studied in 2 successive years. Low body condition score at calving (3.5f 0.1, scale 1-9) was associated with prolonged post-partum anoestrous intervals in suckled cows, but provided cows were maintaining liveweight, ovarian cyclicity resumed within 50 days if calves were weaned 70 days post-partum. This response to weaning was totally inhibited in cows that calved in low body condition that lost liveweight post-partum (Year 1). In contrast, marked levels of post-partum liveweight loss (23%) did not affect resumption of ovarian cyclicity in response to weaning (at 50 days post-parturn), or time to conception, among cows that calved with high body condition scores (5.8 � 0.2, Year 2). Reduced milk yields and calf weight gains among underfed cows were associated with higher suckling frequencies and durations ( P < 0.05). Acyclic interval after weaning was negatively related to body condition score at weaning (P < 0.01), and positively related to preweaning suckling intensity (P < 0.01). The time taken to resume ovarian cyclicity after weaning increased by a factor of 1.2 for every half unit decrease in body condition score at weaning, and by a factor of 1.3 for every 30-min increase in time suckled per day prior to weaning. Within level of nutrition, higher frequencies and durations of suckling were associated with higher plasma prolactin levels. Plasma IGF-1 levels were consistently depressed in underfed cows, whereas plasma insulin and GH levels were less affected by nutritional treatments. Effects of undernutrition in suckled cows appear to operate at least partly through interactions with milk yield and suckling intensity. Management of post-partum anoestrus in Bos indicus cows should focus on the conservation of cow body condition and on the strategic use of early weaning.

The performance of Brahman-Shorthorn and Sahiwal-Shorthorn beef cattle in the dry tropics of northern Queensland. 5. Scrotal circumference, temperament, ectoparasite resistance, and the genetics of growth and other traits in bulls

The genetics of growth to 24 months, scrotal circumference (SC) at 24 months and temperaments at 6, 12 and 18 months in 7 year groups of F2 et seq., 1/2 Brahman, 1/2 Sahiwal, 3/4 Brahman and 3/4 Sahiwal bulls were investigated in the dry tropics of northern Queensland. Cattle tick (Boophilus microplus) and buffalo fly (Haematobia irritans exigua) resistance were also assessed at 24 months. Scrotal circumference at 24 months was highest in 1/2 Sahiwal crosses (28 cm v. 26-27 cm; P<0.05) with pronounced variation between years (24-31 cm; P<0.05). Temperaments (TEM score; flight distance) were generally poorest in 3/4 Sahiwal crosses (P<0.05). Bulls of 1/2 Bos indicus content were twice as susceptible as 3/4 crosses to tick infestations (P<0.05). There were no genotype differences in natural buffalo fly infestations. Temperaments, tick resistance and buffalo fly resistance all had no consistent significant relationships with either each other or with weights or growth rates to 24 months. Paternal half-sib estimates of heritabilities across all genotypes were generally moderate for weight (0.20-0.36), growth rates (0.08-0.46), and SC (0.32), low for TEM score (0.08-0.14), and high for flight distance (0.32-0.70). The genetic correlations (rG) between growth rates in both dry and wet seasons after weaning were high (>0.9); however, the rG of weaning weight with postweaning seasonal growth rates to 24 months were consistently negative (-0.09 to -0.71; P>0.05). The rG of SC with post-weaning growth rates were negative (-0.4 to -0.8). The rG of SC with weights up to 18 months were not significantly different to zero, but tended to be negative with weight at 24 months.

Hormone concentrations in the caudal vena cava during the first ovarian follicular wave of the oestrous cycle in heifers

Changes in pulsatile secretion of LH, FSH, oestradiol and progesterone were related to the growth phase, early plateau phase and regression phase of the first ovarian dominant follicle of the oestrous cycle in Bos indicus heifers. Relationships between these hormones during the three phases were also investigated. Accurate measurements of episodic ovarian steroid secretion were obtained by catheterizing the caudal vena cava via the lateral saphenous vein; the tip of the catheter was positioned just cranial to the ovarian vein using transrectal ultrasonography. Pulsatile secretion of oestradiol was increased only during the growth phase of the dominant follicle and was associated with high frequency release of LH pulses. However, mean concentrations of oestradiol were reduced when the dominant follicle attained its maximum diameter. Between the growth and plateau phases, as the amount of progesterone released increased and oestradiol released decreased, LH pulse frequency and mean concentration of LH decreased. Pulses of LH released were followed within 15 min by increases in mean concentrations of oestradiol (P < 0.001); however, there was no apparent relationship between LH and progesterone release (P = 0.19). Although there was little evidence of pulsatile release of FSH, mean concentrations of FSH were increased by 0.2 ng ml-1 (P = 0.04) during the plateau phase, which was on average 2.1 days before the day of emergence of the second dominant follicle of the oestrous cycle. This increase in FSH, in conjunction with the decrease in secretion of oestradiol, may be an indication of the loss of functional dominance by the first dominant follicle of the oestrous cycle.

Sequential changes in ovarian follicular dynamics in Bos indicus heifers before and after nutritional anoestrus

This study examined the effects of live mass on ovarian follicular dynamics in heifers before and after the onset of nutritional anoestrus. The effects of decreased live mass on secretion of progesterone, LH and FSH were also investigated. Ovarian characteristics were monitored in 16 postpubertal Brahman heifers using daily transrectal ultrasonography. After two normal oestrous cycles, 11 heifers (treatment group) were allocated to a restricted diet, until the cessation of their oestrous cycles, that resulted in a decrease in live mass of 0.8 kg day-1. Heifers were then fed an ad libitum diet, resulting in increasing live mass until resumption of oestrous cycles. Five heifers (control group) were fed an unrestricted diet throughout the experimental period. The concentrations of progesterone in plasma were monitored twice a week and the concentrations of LH and FSH were determined on day 6 after ovulation, before initiation of dietary restriction, after a 17% decrease in live mass and after the onset of anoestrus in the treatment group. Onset of anoestrus was preceded by linear decreases in the size of ovarian follicles and corpora lutea, and in the persistence of the first dominant follicles of oestrous cycles. These changes were proportional to the decrease in live mass (P < 0.001). The frequency of pulses of LH or mean concentration of FSH on day 6 of the oestrous cycle were not changed after a 17% decrease in live mass, and did not increase following the onset of anoestrus, although concentrations of progesterone were < 0.2 ng ml-1, suggesting that release of LH was suppressed at this time.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma progesterone and blood metabolite profiles in post-partum small east African zebu cows

Plasma progesterone profiles were used to monitor post-partum reproductive activity in 12 Small East African zebu (Bos indicus) cows allocated to either supplementary or no supplementary feeding (control) with continuous or restricted (twice daily) suckling regimes. Intact bulls were used for breeding. Blood samples were collected 3 times a week for 33 weeks to determine plasma progesterone levels. Weekly blood samples were also used to determine blood metabolite concentrations. Plasma progesterone levels remained below 1 ng/ml in all cows until week 12 post-partum. Only 5 cows showed ovarian activity over the 33 week period. Cows that cycled expressed irregular and short-lived progesterone rises (> 1 ng/ml) lasting 8 to 12 days prior to establishment of normal patterns of progesterone secretion where progesterone levels ranged from 8 to 10 ng/ml in cows with normal cycles. Plasma total protein, albumin, globulin, blood urea nitrogen and glucose levels varied over time without consistent trends, and were not influenced by either supplementary feeding of suckling regimes, nor differed between cyclic and acyclic cows. It was concluded that extended post-partum anoestrus, conception failure and early embryonic mortality were responsible for lowered reproductive efficiency in zebu cows. Blood metabolite concentrations were not good indicators of nutritional status and were not related to post-partum ovarian activity.

Reducing post-partum anoestrous interval in first-calf Bos indicus crossbred beef heifers. 2. Responses to weaning and supplementation

Supplementation designed to increase the supply of glucose and amino acids, was compared with early weaning as strategies for reducing post-partum anoestrous in Bos indicusx Bos taurus (518x318) first-lactation heifers. Twenty-three pregnant heifers were allocated to four treatment groups and fed long-chopped hay (15.8 g N/kg dry matter) ad libitum and a complete mineral mixture throughout the experiment as well as 450 g molasses and 50 g urea per day during the final month of pregnancy. After calving, three groups were supplemented daily for 120 days with either 2 kg cracked rice (E), 0.4 kg formaldehyde-treated casein (P), or cracked rice (2 kg)+formaldehyde-treated casein (0.4 kg) (E+P); the unsupplemented control group had their calves weaned at 60 days post-partum. Supplemented animals had significantly higher intakes of hay (7- 1-7.3 v. 5.9 kg OM/day), weight gain (0.4-0.5 v. 0.0 kg/day) and body condition score (4.6-4.7 v. 4.3) than the unsupplemented heifers, but there were no differences between the supplemented groups in these variables. Unsupplemented animals and heifers fed P partitioned similar amounts of lactose and fat into milk, whereas secretion of both lactose and protein was significantly higher in the E+P and E groups. All control heifers ovulated within 14 days of their calves being weaned, whereas only two of the lactating supplemented heifers (EfP) showed cyclic ovarian activity at that time and three other lactating heifers ovulated several weeks later. The response to weaning occurred in heifers that had a liveweight and condition score of 374 kg and 4.3 respectively, which was 30-50 kg and a half unit in condition below the suckling heifers. In unsupplemented heifers showing ovarian cyclicity, acetate entry rate was less than half that of the supplemented animals, whereas glucose entry rate, adjusted for loss to lactose, was similar for both groups. Supplementation did not affect either the basal concentration or frequency of pulsatile release of luteinizing hormone (LH) at 60 days post-partum, or the LH response to gonadotrophin releasing hormone (5 8g GnRH). It is concluded that under the conditions of the present study, weaning had a greater effect than post-partum nutritional supplements on the resumption of ovarian activity in first-lactation heifers with moderate nutrition.

Response in female fertility and calf growth to selection for pregnancy rate in tropical beef cattle

Direct response to divergent selection based on estimated breeding value for female pregnancy rate in a herd of Bos indicus cross cattle was evaluated along with correlated responses in calf survival, weaning rate, cow liveweight and calf growth. Pregnancy rates were significantly higher ( P < 0.05) in heifers of the High line compared with the Low line (High-Low=15� 5%) and in lactating 4-year-old cows (25�9.5%) and in 3 of the 5 years of the study (average difference 24%). The Low line had significantly ( P < 0.05) higher pregnancy rates in 1 year (-16�5.4%). These differences in pregnancy rates were reflected in weaning rates, but calf survival was only different between the lines in 2 of the 4 years analysed (-6� 3.0% in 1990 and 18�6.5% in 1991). The High line had a significantly ( P < 0.05) shorter days to calving than the Low line in heifers (High=309�2.2 days v. Low= 315�2.5 days), lactating 3-year-old cows (3l5� 3.6 days v. 331�4.1 days), non-lactating 3-year-old cows (301�5.4 days v. 320�4.6 days) and lactating 4-year-old cows (311�3.9 days v. 336�4.9 days). Differences between the lines in pre-weaning growth varied according to generation with significantly lower (P < 0.05) weaning weights (182�3.1 kg v. 189�3.3 kg) and pre-weaning growth (790�17 g/day v. 826� 17 g/day) in first generation High line calves from foundation dams and no difference between the lines in second generation calves from first generation dams. Post-weaning growth was significantly higher ( P < 0.05) in High line calves (350� 5 g/day v. 327�5 g/day). The results indicate that selection of sires on EBV for pregnancy rate leads to improved fertility in heifers and 4-year-old lactating cows without adverse effects on progeny growth.

Reducing post-partum anoestrous interval in first-calf Bos indicus crossbred beef heifers. 1. Effects of pre- and post-partum supplementation strategies

The effects of pre-and post-partum (ppp) v. post-partum (pp ) supplementation on reproductive function were compared in Bos indicus x Bos taurus (5/8 x 3/8) first-calf heifers. Twenty-four pregnant heifers were allocated to three treatment groups all fed roughage hay ad libitum. The dietary treatments were: (1) nil supplement controls, (2) cracked maize (1 kg) plus formaldehyde treated sunflower seed meal (0.5 kg) daily for 60 days post-partum, (3) supplement 2 from 1-2 months pre-partum to 60 days post-partum. Supplementation did not affect hay intake prior to calving (6.5 kg/day), but significantly increased (P < 0.05) intake by approximately 50% after calving compared with a 20% increase in the controls. Maternal liveweight, adjusted for the weight of the foetus and gravid uterus, was 345 kg in all groups at 5 weeks before calving. This weight declined by 6 kg in unsupplemented animals and increased by 16 kg with supplementation before calving. During the 2 months after calving, ppp supplemented animals maintained weight, pp supplemented heifers gained 26 kg, and controls lost 39 kg. Birth weight of calves from heifers supplemented before parturition was 34.2 � 1.9 kg, 5.6 kg heavier than the other calves (28.64�0.7 kg). Milk yield and N secretion tended to be highest in ppp supplemented heifers in the peri-partum period. Two months after calving, milk yield and secretion of N, fat and lactose were not different in both supplemented groups, but were significantly higher (P < 0.05) than in the controls. Endogenous pulsatile release of LH and FSH was not detected in heifers from any group 50 days after calving. Following GnRH injection (100 8g, i/m), the LH response was not significantly different between groups, but the unsupplemented animals had greater ( P < 0.05) FSH responses than the supplemented heifers. Supplemented heifers had lower ( P = 0.07) plasma GH concentrations prior to calving; after calving, GH levels were in the order: ppp supplemented < pp supplemented < controls. There was no indication that supplementation affected ovarian folliculogenesis in animals treated with exogenous gonadotrophin, and all animals were in an anoestrous state at 60 days post-partum. In conclusion, the type of supplementation practiced here did not appear to improve reproductive performance in first-calf heifers weighing 340-360 kg in early lactation. However, ppp supplementation was the most effective treatment in reducing GH levels and maintaining liveweight in the peri-natal period, both of which have been associated previously with reducing post-partum anoestrous interval.

Seasonal influences on gonadal and extragonadal sperm reserves in Small East African zebu (Bos indicus) bulls in Ethiopia

Body weight and scrotal circumference (SC) data were taken ante mortem and genitalia collected after slaughter from Small East African zebu (SEAZ) bulls slaughtered during the wet (n = 46) and the dry (n = 53) seasons. Bulls slaughtered during the wet season were significantly heavier (47 kg) and had significantly larger SC measurements (3.3 cm) than those slaughtered during the dry season. Mean (+/- s.e.m.) paired testes weights were 233.7 +/- 13.8 and 292.8 +/- 11.3 g and epididymal weights 26.8 +/- 0.9 and 35.9 +/- 1.1 g in bulls slaughtered during the dry and wet seasons, respectively. Daily sperm production rates and epididymal sperm reserves were 2.2 +/- 0.1 x 10(9) and 3.0 +/- 0.1 x 10(9); and 16.1 +/- 0.3 x 10(9) and 17.6 +/- 0.4 x 10(9) in bulls slaughtered during the dry and wet seasons, respectively. These differences were significant. It was concluded that season affected reproductive capacity of zebu bulls probably due to variations in the quality and quantity of nutrition. However, the confounding effects of ambient temperature and nutrition on reproductive capacity of zebu bulls in tropical regions need further examinations.

Effects of supplementary feeding and suckling intensity on postpartum reproductive performance of small East African Zebu cows

Small East African Zebu cows (n = 120) which calved during the dry season were used to determine the effects of postpartum nutritional supplementation and suckling intensity on body weight, body condition score, reproductive performance and on calf mortality and preweaning growth performance. Cows were allocated based on calving body weight to either receive a supplementary feed of molasses blocks containing 10% urea or to serve as controls and to be grazed only. Within nutritional groups, cows were further assigned either to continuous suckling or to restricted suckling twice daily. Intact bulls were introduced 21 days after the first cow had calved, and data were collected for 8 months. Calving body weight and body condition score of dams ranged from 186 to 192 kg and from 3.8 to 4.2 and did not differ among the treatment groups. Supplementary feeding significantly (P<0.05) reduced calf mortality from 40 to 20%, while restricted suckling reduced mortality by 13% from 36 to 23%. Body weight and body condition score did not vary between groups during the supplementation period. Over the 8-month period, 65% of supplemented and 53% of control cows exhibited estrus (P>0.05). A significantly (P<0.05) karger percentage of restricted suckled cows showed estrus than of continuously suckled cows (74 vs 42%). The postpartum estrus interval was shorter by 54 days in supplemented than in control cows and by 13 days in restricted than in continuously suckled cows. The pregnancy rate was higher in supplemented than in control cows (37 vs 33%; P>0.05) and in restricted than in continuously suckled (46 vs 22%; P>0.05) cows.

Effects of dry season nutritional supplementation on growth, onset of puberty and subsequent fertility in Boran and Boran × Friesian heifers in Ethiopia

Shortly after weaning at 8 months of age, 43 Boran and 46 Boran x Friesian crossbred heifers were randomly divided to either receive a supplementary feed containing 16% crude protein during the dry season or to serve as controls. Heifers were examined monthly, and data on body weight, wither height and body condition score were recorded. Ovarian size and structures were determined per rectum and heifers were kept under continuous observation for standing estrus. Blood samples were collected at 10-day intervals every month for determination of plasma progesterone levels. All heifers were exposed to intact bulls for 4 months after they attained 18 months of age. Average daily weight gain to puberty was significantly (P<0.01) higher in heifers given supplementation than in the controls (360 vs 326 g/day). The average daily weight gain in Boran heifers (296 g/day) was significantly (P<0.01) lower than in crossbred (392 g/day) heifers. Mean age at puberty differed significantly (P<0.001) between heifers given supplementation (573 days) and the controls (627 days). Boran heifers attained puberty at a significantly later age (660 vs 540 days; P<0.001) than crossbred heifers. Body weight at puberty did not differ between supplemented and control heifers (226 vs 222 kg); while the difference between Boran and crossbred heifers was significant (216 vs 232 kg; P<0.01). Pelvic size and body condition score were not influenced by supplementation but differed significantly between genotypes. Pregnancy rate after 4 months of breeding was higher in supplemented (79%) than in control (64%) heifers. Boran heifers had a significantly (P<0.001) lower pregnancy rate than crossbred heifers (52 vs 91%). Mean age and body weight at conception were not affected by supplementation but differed significantly (P<0.05) between genotypes. The results indicate that prepubertal supplementary feeding during the dry season increased growth rate, reduced age at puberty and improved fertility in both Boran and Boran x Friesian heifers.

Nutritional influences on growth and onset of puberty in Boran and Boran × Friesian bulls in Ethiopia

Twenty-seven Boran and 37 Boran x Friesian crossbred bulls were weaned at 6 months of age and randomly assigned to either a dry season supplementary feed containing 16% crude protein or control groups. Data were collected on body weight, wither height and scrotal circumference (SC) at monthly intervals. Bulls were also challenged with 100 mug of gonadotropin releasing hormone (GnRH) at 2-month intervals and plasma testosterone responses were determined. Semen was collected at monthly intervals by electroejaculation. Post weaning average daily weight gain was significantly (P<0.001) higher in supplemented than in control groups (302 vs 208 g/day). Scrotal circumference growth rates were also significantly (P<0.001) higher in supplemented than in control bulls (0.38 vs 0.31 mm/day). Bulls fed supplemented diets were younger (430 vs 473 days; P<0.001) and heavier (217 vs 203 kg; P<0.05) and had better semen quality at puberty than the control bulls. There was a trend for larger SC at puberty in supplemented than in control bulls (P=0.06). There were no significant differences in wither height or in testosterone response to GnRH at puberty between supplemented and control bulls. Body and SC growth rates to puberty for Boran and Boran x Friesian bulls were 189 and 321 g/day (P<0.001) and 0.27 and 0.42 mm/day (P<0.01), respectively. Boran bulls were older (513 vs 406 days; P<0.01) and lighter (201 vs 215 kg; P<0.05), and had smaller SC (23.9 vs 26 cm; P<0.01) at puberty than Boran x Friesian bulls. Testosterone responses to GnRH increased (P<0.001) with age and were significantly higher (P<0.05) in supplemented and in Boran x Friesian bulls than in control and Boran bulls. Wither height, testosterone response to GnRH and semen quality at puberty did not differ between breeds. Dry season supplementation improved growth rate and enhanced sexual development and maturity in both Boran and Boran x Friesian bulls, and would be a useful management strategy for enhancing fertility in bulls in the tropics.

Fetal development and gestational changes in and genotypes in the tropics

Weights of the gravid uterus and fetus as well as the fetal measurements were determined at slaughter for 107 Bos taurus cows grazed on improved pastures and for 70 Bos indicus cows grazed on native pastures in northern Australia. The stage of gestation was assessed from palpation per rectum in early-to-mid gestation and at slaughter and from fetal development characteristics at slaughter. The age and breed of the cow and the sex of the fetus did not significantly affect any of the uterine components or fetal measurements. Growth curves had dominant, positive linear components but negative quadratic ones, which improved the fit, particularly for the later stages of gestation. Uterine components and fetal measurements were highly correlated (0.94 to 0.99). For Bos taurus cows, there were higher estimates at birth for weights of the gravid uterus and the fetus, but estimates for other fetal measurements were similar to those for Bos indicus cows. Major fetal growth occurred during the third trimester, with the length of the foreleg tending to change relatively slowly and the head width quite fast during the first trimester. Correction factors for cow liveweight to adjust to commonality for non-pregnancy were 5, 7, 10, 14, 20, 29, 43 and 65 kg for Bos taurus and 2, 4, 6, 10, 15, 23, 35 and 51 kg for Bos indicus at 2 to 9 months of gestation.

A quantitative histological study of testicular and epididymal development in Boran and Boran × Friesian bulls in Ethiopia

Quantitative histological techniques were used to characterize the pattern of testicular and epididymal development in 42 Boran and 49 Boran x Friesian bulls aged between 6 and 23 mo. Bulls were divided into five age groups having four-month intervals. Between 6 and 23 mo of age, body weight increased from 124 to 293 kg and 179 to 267 kg (P<0.01) in Boran and Boran x Friesian bulls, respectively. Scrotal circumference measurements increased from 6 to 23 mo by 10.2 and 8.9 cm in Boran and Boran x Friesian bulls. Paired testes weight increased significantly (P<0.001) over the same period from 29 to 304 g and 59 to 291 g in Boran and Boran x Friesian bulls, respectively. Both caput and cauda epididymal segment weights also increased significantly (P<0.001) with age. There were significant (P<0.05) genotype differences in seminiferous tubule diameter, which increased by 137 and 90 microm with increasing age in Boran and Boran x Friesian bulls, respectively. Patent seminiferous tubules were first observed at 206 and 188 d of age in Boran and Boran x Friesian bulls, respectively. The appearance of elongated spermatids and spermatozoa in the seminiferous tubules and epididymal tubules occurred at later ages in Boran than in Boran x Friesian bulls.

The development of puberty and sexual maturity in the Australian Swamp buffalo bull

Testes from 47 juvenile Swamp buffalo bulls were examined for puberty and sexual maturity histologically and daily sperm production per gram of testis parenchyma was determined by enumeration of elongated spermatids in homogenates of testis parenchyma. Puberty was defined as the attainment of a daily sperm production per gram of testis parenchyma>0.5x10(6). In most bulls, puberty is attained by 24 mo of age, when scrotal circumference (SC) is approximately 16 cm, and liveweight exceeds 135 kg. Sexual maturity was defined as the attainment of adult levels of daily sperm production per gram of testis parenchyma (14x10(6)). In most bulls, this occurs at 30 to 33 mo of age, when SC is in the 17-to 20-cm range, and liveweight generally exceeds 250 kg. There was marked individual variation in age, liveweight and SC at both puberty and sexual maturity.

The effects of capture stress on testis function in the Australian Swamp buffalo ()

Capture stress significantly affected the cellular composition and function of the testis and epididymis of feral Swamp buffalo bulls. There was an initial acute drop in the population of elongated spermatids, round spermatids and late primary spermatocytes, and subsequently, a more gradual decline in the early elongated spermatid and late primary spermatocyte populations as the duration of the stress increased. Sertoli cell numbers were unaffected. The most marked effect was on the early elongated spermatid population, which was approximately halved in the stressed bulls. Testis parencyhmal weight was approximately 50% lower in stressed bulls. Affected bulls would undoubtedly be at least temporarily subfertile or infertile. The long-term prognosis on the fertility of such bulls is not known. Possible mechanisms involved in the pathogenesis of the syndrome are considered in this study.

Reproductive function in the Australian Swamp buffalo bull: Age effects and seasonal effects

Swamp buffalo exhibited seasonal variations in daily sperm production and in daily sperm production per gram of testis parenchyma. Maximum rates occurred in the late wet season and early dry season. There was no spermatogenesis detected in 1-yr-old bulls. Daily sperm production per gram of testis parenchyma increased thereafter up to 3.5 yr of age, and was similar in all older age groups. Scrotal circumference in bulls of this age ranged from 20 to 21 cm. Scrotal circumference and daily sperm production increased rapidly up to maturity, and increased less rapidly thereafter. Mean+/-SEM daily sperm production per gram in 146 mature buffalo bulls was 14.04 x 10(6)+/-0.39 x 10(6) and mean+/-SEM daily sperm production was 1.86 x 10(9)+/- 0.07 x 10(9). Mean+/-SEM epididymal sperm reserves in adult bulls numbered 9.7 x 10(9) +/- 0.07 x 10(9). These were distributed between the caput, corpus and cauda epididymis in the proportions of 28.82, 14.63 and 60.55, respectively. Mean+/-SEM epididymal transit time was 5.65+/-0.24 d.

The cycle of the seminiferous epithelium in the Australian Swamp buffalo

The relative frequencies of stages and substages of the Swamp buffalo seminiferous epithelium were determined using a morphological classification. Duration of one cycle of the seminiferous epithelium was determined from radiolabelling studies using tritiated thymidine. Mean (+/-SD) duration of the cyle of the seminiferous epithelium of five Swamp buffalo was 8.74 +/- 0.18 d. Mean (+/-SEM) relative frequencies of stages and substages of the seminiferous epithelial cycle in ten bulls were Stage 1a, 7.27 +/- 0.72; Stage 1b, 8.11 +/- 0.85; Stage 1c, 8.54 +/- 1.13; Stage 2a, 5.9 +/- 0.79; Stage 2b, 7.49 +/- 0.78; Stage 3a, 9.05 +/- 0.66; Stage 3b, 9.69 +/- 1.11; Stage 4a, 5.04 +/- 0.44; Stage 4b, 4.8 +/- 0.69; Stage 5, 1.86 +/- 0.23; Stage 6, 8.81 +/- 0.84; Stage 7, 10.64 +/- 1.2; Stage 8a, 6.87 +/- 0.96; and Stage 8b, 5.93 +/- 0.72.

Epidemiological studies of bovine spumavirus

Bovine spumavirus (BSV) infection is shown to be endemic in some herds in north Queensland. The virus was readily isolated from leucocytes of the majority of mature cattle which were BSV antibody positive (BSV reactors) in the agar gel precipitin test (AGPT). Calves born to dams which were BSV reactors showed no BSV antibody or circulatory leucocyte-associated BSV (CLAB) at birth, but became BSV reactors following ingestion of colostrum, and maintained such evidence of passive immunity until 3-5 months of age. Experimental infection of dams with BSV at 5-7 months of gestation did not cause foetal infection. In groups of young animals at pasture, segregated by age and sex, no evidence of BSV infection occurred, following loss of passive immunity, until 18-24 months of age. At this time, occasional members of some groups (both male and female) became BSV reactors and showed CLAB. At approximately 24 months old, following mixing in groups with older cows, and single-sire mating, 34% of heifers became BSV reactors within 10 weeks. A herd survey indicated 85% of 2-3-year-old cows to be BSV reactors; thereafter, the percentage of reactors declined gradually with increasing age. Using BSV grown in cell culture, transmission of infection by throat spray was the most successful route, 7 of 7 (100%) of susceptible cattle becoming BSV reactors within 8 weeks of spraying. Using the intravenous route, only 2 of 5 (40%) susceptible cattle became BSV reactors, and swabbing of cell culture virus into the prepuce or vagina did not result in infection of 4 BSV-susceptible animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Patterns of puberal development in Sahiwal and Brahman cross bulls in tropical Australia

Plasma LH and testosterone (T) concentrations were measured before (basal) and two hours after (peak) GnRH stimulation in 52 Bos indicus strain bulls between one and two years of age. The animals comprised 13 1 2 Brahman, 20 3 4 Brahman, 8 1 2 Sahiwal and 11 3 4 Sahiwal cross bulls and samples were collected at approximately seven week intervals. Basal- and peak-T concentrations increased between one and two years of age, and basal LH concentrations decreased; no changes in peak LH were noted over time. Peak-T concentrations were significantly correlated with scrotal circumference (SC), sperm per ejaculate and seminal fructose. Significant genotype differences were noted, Sahiwal cross bulls had higher peak-T concentrations at puberty than Brahman cross bulls.

Patterns of puberal development in Sahiwal and Brahman cross bulls in tropical Australia. I. Growth and semen characteristics

Reproductive development was monitored in 13 1 2 Brahman (BX), 20 3 4 BX, 8 1 2 Sahiwal (SX) and 11 3 4 SX crossbred bulls between one and two years of age. Liveweight increased during wet season (0.7 kg/day) and decreased during dry season conditions (-0.25 kg/day). Scrotal circumference (SC) increased from 18.6 to 25.0 cm, but decreased slightly during the later stages of the dry season. First ejaculates containing 50 x 10(6) spermatozoa were obtained from 25% of the bulls at 15.3 months of age and from 84% by two years of age. Sperm motility and morphology showed no consistent pattern, but number of sperm per ejaculate increased and seminal fructose concentrations decreased with advancing age. Significant genotype differences were noted for SC and seminal characteristics. Estimated age and liveweight at puberty were 570, 563, 578 and 542 days, and 251, 265, 247 and 256 kg for 1 2 BX, 3 4 BX, 1 2 SX and 3 4 SX bulls, respectively.

Seminal shedding of bluetongue virus in experimentally infected mature bulls

Sixteen bulls ranging in age from 2 to 11 years were experimentally inoculated with bluetongue virus to investigate the frequency and duration of seminal shedding of the virus. All bulls developed typical viremia, lasting 21 to 58 days, and they seroconverted 2 to 3 weeks after inoculation. Virus isolation was attempted from a total of 232 ejaculates, 163 (70%) of which were collected during the period of viremia. Bluetongue virus was not isolated from any of the ejaculates collected from 11 of the 16 bulls. Virus was isolated from 9 of 52 ejaculates collected from the other 5 bulls during the period of viremia. In no instance was virus isolated from semen without concurrent isolation from blood.

Spermiogram and sperm reserves in hybrid Bos indicus X Bos taurus bulls after scrotal insulation

Scrotal insulation for 48 h raised subcutaneous scrotal temperature by 4 degrees C in hybrid Bos indicus X Bos taurus bulls. The incidence of decapitated spermatozoa in the ejaculate increased significantly between 6 and 14 days and that of protoplasmic droplets and tail abnormalities between 20 and 23 days after insulation, respectively. Simultaneously, the percentages of spermatozoa with lost and damaged acrosomes increased significantly 12-17 days after insulation. At slaughter 23 days after scrotal insulation sperm production rates and gonadal reserves had not been affected by insulation, but epididymal reserves were markedly reduced, particularly in the cauda. Elevated testicular temperature therefore had an effect on immature spermatozoa in the caput epididymidis and on spermatids, but it is suggested that selective sperm resorption in the rete testis and excurrent ducts may prevent some of these changes being expressed in the ejaculate.

The supplementary feeding of sheep consuming Mulga (Acacia aneura) with low levels of molasses and urea under field conditions

Mature Merino wethers grazing mulga (Acacia aneura) in south-west Queensland were supplemented for 21 weeks with 50 or 100 g DM molasses day with or without 6 g urea day -' .Growth rates and clean fleece yields in the supplemented groups were higher (P < 0.05) than in unsupplemented controls. The control group lost liveweight during the experiment. Growth rates and clean fleece yields were higher (P < 0.05) in groups receiving 100 g DM molasses day -' than in the groups receiving 50 g DM molasses day-'. Provision of urea depressed (P <0.05) growth rates and clean fleece yields. Differences were not as evident when comparing clean wool production per unit area and fibre diameter: significant (P <0.05) differences only occurred between the two levels of molasses supplernentation. Fibre diameter was larger in each of three measure- ment periods and clean wool production per unit area was higher in the middle measurement period for groups receiving 100 g DM molasses day -' .

Duration of the seminiferous epithelial cycle in hybrid Bos indicus x Bos taurus bulls

The hybrids were carrying 50% (N = 4) or 75% (N = 4) zebu (Brahman) blood. The spermatogenic cells were labelled in vivo with [3H]thymidine. The relative frequencies of the seminiferous epithelial cycle stages, determined from examination of 6350 tubule cross-sections, did not differ between the 2 hybrid types examined, between regions of the testis or between testes within animals. Frequencies were generally similar to those for Bos taurus bulls except that the frequency of stage 4 tubules was lower and that of stage 8 tubules higher. The mean duration of the seminiferous epithelial cycle was 13.41 days and was similar for both types of hybrid. The durations of meiosis and spermiogenesis were calculated to be 20.7 and 17.4 days respectively, estimates which are similar to those for Bos taurus bulls. From the relative frequency of cell stages and estimates of the duration of the cycle, a time divisor of 5-11 days is suggested as being appropriate to determine daily sperm production from counts of spermatid reserves in testicular homogenates of these hybrid bulls.

Quantitative macroscopic and histological study of testicular hypoplasia in Bos indicus strain bulls

Forty-six bulls between 17 and 23 months old were used in an investigation of testicular hypoplasia in Bos indicus strain bulls. Testes diagnosed as either unilaterally or bilaterally hypoplastic or normal were obtained at castration and were examined macroscopically and by quantitative histological methods. Estimations of sperm per gram of testis (spg) were made on these 46 bulls and two others. Testis weight was greatest in the 'normal of unilateral' group (106 g). The mean epididymis:testis weight ratio was 0.12 and did not differ significantly between groups. Increased basement membrane thickness, increased vacuolation and giant cells were not features of testicular hypoplasia per se. Seminiferous tubule diameter varied from 118 micrometer in bilaterally hypoplastic testes to 171 micrometer in normal testes. A mean tubule diameter of about 150 micrometer was considered useful for differentiating hypoplastic from normal testes in young post-puberal B indicus crossbred bulls. There was a significant correlation between tubular diameter and spg (r = 0.68, P less than 0.001) suggesting that tubular diameter measurements in histological sections could be used to predict sperm production. Although there was good agreement between clinical diagnosis and spg values, high spg values were found in several small testes which were considered hypoplastic on clinical examination. Examination of both unilaterally and bilaterally hypoplastic testes showed an interesting variation in the ratio of nucleus to cytoplasm in the interstitial cells. This was significantly (p less than 0.05) lower in the testes of normal bulls than in the other clinical groups.

The effect of scrotal insulation on spermatozoal morphology and the rates of spermatogenesis and epididymal passage of spermatozoa in the bull

In five beef bulls spermatogenic cells labelled with (3)H-thymidine were used to estimate the duration of one cycle of the seminiferous epithelium (S.E.) and epididymal passage (E.P.) of spermatozoa after 10 or 20 hr of scrotal insulation designed to increase testicular temperature. From six autoradiographic estimates in three bulls, the mean value for 1 S.E. cycle was 13.4 days (range 12.9 to 13.6 days). Two estimates of E.P. were both 13.5 days. Scrotal insulation altered both semen quality (lowered percentage live and motile spermatozoa, raised percentage abnormal spermatozoa and lowered concentration per ml spermatozoa) and the histological appearance of the seminiferous epithelium. However, the rate of spermatogenesis and epididymal transport was unchanged.

The nitrogen metabolism of sheep consuming Flinders grass (Iseilema spp.), Mitchell grass (Astrebla spp.) and mixed native pasture

Some aspects of nitrogen metabolism of sheep given Mitchell grass (Astrebla spp.), Flinders grass (Iseilema spp.) and mixed native pasture were investigated. All diets were of low nutritive value as demonstrated by negative nitrogen and energy balances in sheep on these diets. Studies of urea metabolism demonstrated a significant relationship between plasma urea concentration, the rate of irreversible loss of urea from plasma and the rate of urea degradation in the digestive tract. On average, 81% of the urea synthesized in the body was transferred to the digestive tract and degraded to ammonia and carbon dioxide. The proportion of urea degradation occurring intraruminally was estimated during an intravenous infusion of 14C urea by measuring the rate of appearance of 14CO2 in ruminal fluid, the proportion degraded post-ruminally being obtained by difference. Urea degraded in the rumen accounted for 7–13% of the total quantity degraded in the digestive tract, and the rate of urea transfer (0.55 ± 0.13 g nitrogen/day) was not related to the rate of urea synthesis in the body. The lower digestive tract was the major site of urea degradation in sheep given these low protein diets, and the rate of urea transfer to this part of the digestive tract was linearly related to the rate of urea synthesis in the body. The implications of these findings are discussed in relation to nitrogen conservation in sheep given low quality diets.

Observations on squamous cell carcinomas of sheep in Queensland, Australia

Observations were made over a 4-year period on squamous cell carcinomas on the ear and other areas poorly covered by hair or wool, sheep pastured in the hot, dry environment of north-western Queensland. Overall incidence in the flock was higher than in flocks kept at greater latitudes. Increased incidence with advancing age was demonstrated, and ewes appeared to be more susceptible than wethers. Metastases were observed in 4 of 33 affected ewes (12%) submitted to detailed necropsy examination. Measurements of tumour growth in 4 ewes revealed an increase in size of about 3-5 mm per month. Ovine aural squamous cell carcinoma was considered to be a good model for studies on skin cancer in man.

The influence of high ambient temperatures and plane of nutrition on wool growth rates of tropical sheep

The wool production of two groups of tropical Merino sheep subjected to a simulated summer circadian temperature regimen, and fed either high or low quality diets, was compared with that of two other groups under similar nutritional conditions but held at prevailing winter ambient temperatures. The nutritional treatments were imposed for the duration of the experiment; the temperature treatments consisted of a. pre-experimental period of three weeks in which all groups were held at prevailing ambient temperatures b. heat adaptation period of one week in which the heat treatment groups were subjected to gradual increases in the circadian temperature regimen c. heat treatment period of three weeks in which the heat treatment groups were exposed to a circadian temperature regimen in which air temperatures were in excess of 38�C for approximately 7 hours day-1d. post heat treatment period of three weeks in which all groups were held at prevailing ambient temperatures. Temperature treatment had no effect on feed intake or liveweight gain; however, intakes progressively decreased in groups on the low quality diet with a similar decrease in liveweight. Wool growth rates were unaffected by temperature treatment, but were significantly lower in animals on the low quality diet. The possible significance of these results to the wool production of tropical sheep is discussed.

Effects of composition of diluent, method of addition of glycerol, freezing rate, and storage temperature on the revival of ram spermatozoa after deep-freezing

The addition of 6% (vJv) egg yolk to a synthetic diluent [247 mM glucose, 49 mM NaCI, 5 mM KCI, 5 mM phosphate buffer, and 7�5% (vJv) glycerol] improved the survival of ram spermatozoa after deep�freezing. Judging by the activity of spermatozoa after thawing, a single addition of glycerol to the diluted semen at 5�C was as effective as multiple additions giving a graded increase of glycerol concentra-tion over a period of 20 min. Reciprocal replacement of the sodium chloride of the diluent by an increase in the concentration of the phosphate buffer showed that motility of the spermatozoa after thawing was depressed when the level of phosphate exceeded 10 mM.

Effects of the number of spermatozoa and volume of diluted semen on fertility in the ewe

Incidence of pregnancy in artificially inseminated Merino ewes was not significantly affected by dilution of semen with buffered glucose so as to present equal numbers of spermatozoa in different volumes (50 or 200 µI) or by reducing number of spermatozoa per insemination from 100 to 50 million. Respective pregnancy percentages for various volumes and concentrations of semen were: 50 µl, 50 x l06, 48.7%; 200 µl, 50 x l06, 57.1%; 50 µl,100 x l06, 53.8%; 200 µl , 100 x 106 52.9%; 31 µl, 100 x l06 (undiluted control), 60.2%. The percentage of pregnancies was significantly higher among ewes with clear or heavy (v. light) raddle marks left by the teaser rams used to detect oestrus, and among those with a copious flow of vaginal mucus at insemination. The fertility of all semen fell as the interval between collection and insemination increased to 1 hr.

The fertility of Merino ewes artificially inseminated with semen diluted in solutions based on skim milk, glucose or ribose

The fertility of Merino ewes artificially inseminated with semen diluted tenfold in milk or buffered glucose solution was lower than that of a control group of ewes inseminated with the same number of spermatozoa in undiluted semen. By means of centrifugation, the concentration of spermatozoa in the insemination dose of diluted semen was raised to match that of the undiluted semen and then the effect of dilution on fertility was eliminated for the glucose-diluted semen, but not for the milk-diluted semen. Respective percentages of ewes not returning to oestrus and ewes lambing were, after insemination with undiluted semen, 60.5, 46.7; with milk-diluted semen, 55.9, 40.2 and after reconcentration 56.0, 38.0; with glucose-diluted semen, 48.2, 35.3, and after reconcentration 62.1, 46.1. In another experiment, the percentage of ewes lambing after insemination with undiluted semen, with semen diluted tenfold with glucose, and with semen diluted with a ribose mixture and chilled at 5°C for 24 hr were respectively 67.0, 58.0, and 26.1. Both diluents contained 6% (v/v) egg yolk and diluted semen samples were reconcentrated to the original sperm density of the semen immediately before insemination.

Passage, Survival, and Fertility of Deep-Frozen Ram Semen in the Genital Tract of the Ewe

The distribution of spermatozoa in the genital tract was determined in ewes killed 4 hr or 24 hr after cervical insemination with 100 million live spermatozoa from either freshly ejaculated or deep.frozen ram semen. At 4 hr, greater numbers of spermatozoa were present in the cervices, uteri, and fallopian tubes in ewes inseminated with fresh semen than in ewes inseminated with frozen semen. At 24 hr, the numbers of spermatozoa in the uteri and fallopian tubes of ewes inseminated with fresh semen had increased relative to the numbers at 4 hr but no spermatozoa were present in the uterus and fallopian tubes in ewes inseminated with frozen semen.