The epidemiology of subfertility in non-seasonal calving dairy herds in the Camden region of New South Wales: description of population and incidence

OBJECTIVE

To describe biographic, reproductive, production and disease characteristics of 965 Holstein cows from 10 non-seasonal calving dairy herds in the Camden region of New South Wales, and to describe the incidence of subfertility, that is, conception requiring > 2 inseminations, in this population.

DESIGN

A retrospective epidemiologic study.

METHODS

Computer records were used to determine biographic, reproductive, production and disease characteristics in all lactations that commenced between 1 July 1995 and 30 June 1996 and resulted in conception during that lactation. Differences in these characteristics among herds and between primiparous and multiparous cows were examined. The lactational incidence of subfertility for lactations commencing during the study period was determined.

RESULTS

Ten herds with appropriate records and management structures entered the study. Herd size ranged from 86 to 203 lactating cows. Nutritional and reproductive management of these herds was typical of smaller pasture-based herds within the study region. Records from 1320 cows were available, of which 965 were considered suitable for descriptive analysis. Monthly variations in number of cows calving were noted, with number of lactations commenced by primiparous and multiparous cows peaking in January and October, respectively. Significant (P < 0.001) inter-herd differences for all reproductive, disease and milk production outcomes were detected for both the entire population and within primiparous and multiparous subgroups. Of 1041 cows submitted for insemination, 76 failed to conceive. The lactational incidence rate (LIR) of subfertility in all lactations was 21.1% (95% CI 19-24%). and among all cows conceiving was 22.8% (95% Cl 20-25%). The LIR of subfertility in primipara was 24.1% (95% Cl 19-28%) and varied widely between herds (10%-40%). The LIR of subfertility in multipara was 22.2% (95% Cl 20-25%) and also varied widely between herds (7%-46%).

CONCLUSION

Parity and herd of origin should be considered in any further analyses of these data.

The epidemiology of subfertility in non-seasonal calving dairy herds in the Camden region of New South Wales: preliminary investigation of risk factors

OBJECTIVE

To investigate relationships between biographic, reproductive, production and disease traits and subfertility among 965 Holstein cows from 10 non-seasonal calving dairy herds in the Camden region of New South Wales.

DESIGN

A retrospective case-control study

METHODS

Biographical, disease and reproductive data were collated from computerised records for cows with lactations that commenced between 1 July 1995 and 30 June 1996 and univariable and bivariable associations with subfertility were determined.

RESULTS

Records from 965 cows that conceived were considered for risk factor analyses. Associations between subfertility and a number of risk factors (P < 0.3) were detected. Significant (P < 0.05) risk factors for subfertility in multiparous cows included herd of origin and, after controlling for the effect of herd, subfertility in the previous lactation, greater than 62 days dry, parity greater than five, interval between calving and first recorded heat, metritis and cystic ovarian disease. Herd of origin and, after controlling for herd effects, dystocia, metritis and percentage of milk fat plus protein at the time of first service were significant (P < 0.05) risk factors for subfertility in primiparous cows. The direction and magnitude of these associations are presented.

CONCLUSION

Subfertility has a similar rate of occurrence in the herds examined to that reported overseas. Although herd of origin has a substantial effect on individual risk of subfertility, cow-level risk factors for subfertility are likely to exist. Exposures differ between primiparous and multiparous cows.

Risk factors for repeat-breeder syndrome in New South Wales dairy cows

A retrospective case-control study involving 1041 cow lactations from 10 commercial dairy herds in Australia determined relationships between biographic, production, reproductive and disease factors and repeat-breeder syndrome (RBS) (conception to greater than two inseminations). The study population was stratified into primiparous- and multiparous-cow sub-groups and logistic regression was used. Effects of herd were examined by including this variable alternatively as a fixed and a random effect. In the primiparous-cow fixed-effect model, the risk of RBS was increased with post-calving metritis, stillbirth, and with increasing days taken to reach peak milk yield, and reduced following dystocia. An inverted U-shaped relationship with total milk-solids percentage at the time of first service was detected. In the multiparous-cow fixed-effect model, the risk of RBS was increased in cows with chronic metritis, cystic ovarian disease (COD), in cows of parity >5 and in cows that were sub-fertile in the previous lactation. Increasing days to first recorded heat (DFH) reduced risk of RBS and a non-linear relationship with average 120-day milk-protein percentage was found. When herd was fitted as a random effect, stillbirth and 120-day average milk-protein percentage were no longer significant in the primiparous and multiparous models, respectively. The study emphasises the need to control appropriately for the clustering effect of herd and supports the need to minimise periparturient disease and improve nutrient balance to achieve optimal fertility in dairy herds.

Association between feeding perennial ryegrass (Lolium perenne cultivar Grasslands Impact) containing high concentrations of ergovaline, and health and productivity in a herd of lactating dairy cows

Perennial ryegrasses are frequently infected with fungal endophyte (Neotyphodium lolii) to increase the resistance of the plant to insect damage. Unfortunately, a side effect of endophyte infection can be the production of alkaloids, including Lolitrem B and ergovaline, that produce toxic effects in animals. A significant 4.6 litre decrease in milk production in a herd of Holstein-Friesian dairy cows was associated with high concentrations of ergovaline in ryegrass silage. Simultaneously, milk SCC increased significantly over a comparable period and reproductive performance declined. Body condition score and coat condition of cows were adversely affected. Unique aspects of this Case report include; very stable production of the herd over a period of years before and after cessation of feeding silage containing high concentrations of ergovaline; the presence of high concentrations of ergovaline in the silage; and a controlled diet that reduced the risks of variation in feed availability and other sources of toxins. Veterinarians and other farm advisors should be aware of the potential for negative effects on animal health and production of fungal endophyte and the potential for Neotyphodium lolii to produce ergovaline.

Uptake of glucose and cholesterol by the ovary of sheep and cattle and the influence of arterial LH concentrations

Time series analysis methods were used to evaluate the relationships between the uptake of glucose and cholesterol, and arterial luteinizing hormone (LH) concentrations. Classical arterio-venous difference methods were applied to study ovarian uptake of metabolites. Arterial and venous samples (n=20) were obtained from six cows and nine sheep every 10min. There were highly significant positive cross-correlations of 0.5 for cattle and 0.8 for sheep between the uptake of glucose and cholesterol at lag 0. All individual cross-correlations were significant for sheep. Uptake of these metabolites was not significantly associated with arterial LH concentrations in the cows. This study suggests that glucose may promote cholesterol uptake into the ovarian cells or vice versa. This study is the first to identify such a relationship. If these findings are repeated, the possibility exists that control of the oestrous cycle and fertility may be achieved by seeking a common regulator of uptake of these metabolites or by uncoupling the association between glucose and cholesterol.

Effects of genetic merit and varying dietary protein degradability on lactating dairy cows

Eighty two multiparous Holstein cows were blocked by genetic merit (high vs. low) and assigned to one of two treatments [high rumen-undegradable protein (RUP): rumen-degradable protein (RDP) vs. low RUP: RDP] from d 21 before to d 150 after calving to study the effects of these treatments on production and reproductive performance. Diets were isonitrogenous (dry cow 10.5% crude protein; lactating cow 19.3%), isoenergetic (dry cow 10.0 MJ of metabolizable energy (ME); lactating cow 10.9 MJ of ME) and fed as total mixed rations. Feeding more RUP significantly increased dry matter intake and milk yield, reduced body tissue mobilization, and lowered concentrations of serum nonesterified fatty acids (NEFA) and plasma urea. Expression of estrus at first ovulation was improved, first service conception rate was higher, and calving to conception interval was shorter for the high RUP group. Cows of high genetic merit produced more milk, mobilized more body tissue, and had higher concentrations of plasma growth hormone. The dry matter intake and concentrations of blood metabolites did not significantly differ with genetic merit. Expression of estrus at first ovulation was significantly lower for cows of high genetic merit. Serum NEFA concentrations were significantly higher, and estrus was not observed at first ovulation for cows of higher genetic merit fed the low RUP diet. The interaction between dietary RUP and genetic merit was not significant for other measures of performance or fertility. Feeding a low RUP: high RDP diet had negative effects on some aspects of production and reproductive performance. The effects of diet on NEFA concentrations and estrus display were greater in cows of high genetic merit, indicating that potential interactions should be evaluated in future reproductive studies involving protein and fertility.

Effects of feeding virginiamycin and sodium bicarbonate to grazing lactating dairy cows

The effects of virginiamycin, an agent active against Gram-positive lactic acid-producing bacteria, and NaHCO3 on ruminal and fecal pH, rumen volatile fatty acid proportions, blood metabolites, and milk production and composition were assessed. This study was conducted over 28 d and involved 71 dairy cows that grazed predominantly ryegrass, oats, and clover, and that were fed 10 kg of concentrate pellets/d per head. The pellets contained (per kilogram) no dietary additive, 30 mg of virginiamycin, 20 g of NaHCO3, or 30 mg of virginiamycin and 20 g of NaHCO3 on a DM basis. Ruminal pH tended to be higher in cows fed pellets containing virginiamycin (7.0 vs. 6.9; SED = 0.16). The results of in vitro incubation of ruminal fluid with glucose found the potential for L-lactic acid accumulation in ruminal fluid to be significantly lower in cows fed virginiamycin (15.5 vs. 35.3 mmol/L; SED = 2.98). Cows fed virginiamycin had significantly higher fecal pH (6.72 vs. 6.57; SED = 0.08) and produced more milk (23.94 vs. 23.32 kg/d) and more lactose than those not fed virginiamycin. No effects of NaHCO3 on fecal pH, in vitro potential for L-lactic acid accumulation in ruminal fluid, or milk production were observed, but ruminal pH tended to be higher and ruminal acetate proportion was greater for cows fed NaHCO3. Milk fat and milk protein percentage did not differ significantly as a result of dietary treatment. These data suggest that the inclusion of virginiamycin in the diet will reduce L-lactic acid accumulation in ruminal fluid and increase fecal pH in grazing dairy cattle fed concentrate supplements.

Relationships among metabolites influencing ovarian function in the dairy cow

Time series analysis was used to evaluate relationships between the uptake of metabolites, ovarian blood flow, arterial LH concentrations, and the output of steroid hormones by the ovary. There were no significant correlations between cholesterol uptake and progesterone output; therefore, cholesterol uptake was not a factor that immediately limited progesterone output. Although no significant correlations were found between cholesterol and oxygen uptake, significant cross-correlations between the uptake of glucose and oxygen by the ovary at lag 0 indicated some immediate oxidation of glucose. This result strongly indicates that glucose is a major source of energy for the bovine ovary. Arterial LH concentrations had little influence on ovarian metabolism. The examination of interrelationships among factors that influence ovarian function was useful in identifying factors that can limit ovarian activity.

Indications and implications for testing of milk urea in dairy cattle: A quantitative review. Part 2. Effect of dietary protein on reproductive performance

DIETARY PROTEIN AND DAIRY COW FERTILITY: Feeding more dietary protein has been negatively associated with dairy cow fertility in some but not all studies. We used meta-analysis to examine the relationship between dietary crude protein and conception rate. While a higher intake of dietary crude protein significantly lowered conception rate, the potential for feeding less degradable dietary protein to modify this relationship was not demonstrated. MILK UREA CONCENTRATIONS AND DAIRY COW FERTILITY: The use of milk urea as an indicator of dietary energy and protein intake and as an indicator of reproductive performance has been questioned. We found that changes in urea concentration in body fluids explained only 25% (p = 0.08) of the variance in conception rate after conducting a meta-analysis of available studies. INTERPRETATION OF MILK UREA CONCENTRATIONS: High intakes of dietary protein may induce adaptations in urea metabolism, and the negative relationship identified between high intakes of dietary protein and fertility for Northern Hemisphere dairy herds may not necessarily apply in Australasian dairy herds. Because of the potential for cows to adapt to high protein diets, the use of a single milk urea determination on a herd will have limited value as an indicator of nutritional status and little value as a predictor of fertility.

Risk factors for culling and deaths in eight dairy herds

OBJECTIVES

To identify risk factors for culling of dairy cows from eight New South Wales dairy herds.

DESIGN

A longitudinal population study of dairy cow culling in eight non-seasonally calving dairy herds in the Camden district of New South Wales. Cox's proportional hazards model was used to evaluate various risk factors for culling for a specific reason (sales, deaths, reproductive failure, disorders of the udder and low milk production).

RESULTS

Age at first calving was not a significant risk factor for culling. Milk production in the first lactation greater than the population mean did not influence length of productive life overall, but was associated with a greater hazard of removal for disorders of the udder. Risk of culling for reproductive failure differed significantly between farms, and was not related to events in the previous lactation such as calving-to-first service interval or calving-to-conception interval. Shorter calving intervals were associated with increased risk of removal for low milk production and disorders of the udder.

CONCLUSION

Longitudinal surveys to accurately identify reasons for removal from a wide range of herds, identification of herds with low culling rates (especially for reproductive failure and udder disorders), and the identification of practices associated with these culling rates would be worthwhile to the Australian dairy industry.

Descriptive epidemiological study on culling and deaths in eight dairy herds

OBJECTIVES

To describe the production and reproduction characteristics of the population under investigation and to compare them with the target population of non-seasonally calving dairy herds, to describe the pattern of culling with respect to length of productive life and length of time after calving, and to identify stages of the production cycle that are associated with increased risk of culling from the dairy herd.

DESIGN

A longitudinal population study of eight non-seasonally calving dairy herds in the Camden district of New South Wales.

RESULTS

The production and reproduction characteristics of this population were broadly similar to herds participating in the New South Wales Agriculture Dairy Herd Improvement scheme. In agreement with recent surveys, risk of culling increased with increased parity. This was accounted for specifically by increased risk of culling for calving disorders, reproductive tract lesions, and disorders of the udder. Risk of culling for failure to conceive appeared to remain constant throughout productive life. The overall risks for culling were greatest during the first 9 days after calving and 300 days after calving.

CONCLUSION

Reducing the incidence of calving-associated disorders, attention to reproductive management and control of herd mastitis offer opportunities to reduce involuntary culling rates in this population.

Indications and implications for testing of milk urea in dairy cattle: A quantitative review. Part 1. Dietary protein sources and metabolism

MILK UREA CONCENTRATIONS IN DAIRY CATTLE: There has been increased use of milk urea concentration as an indicator of dietary protein intake and protein metabolism in dairy cattle over recent years. The value of milk urea content data in predicting dietary composition, particularly for pasture-fed cattle, has not been well described. PROTEIN METABOLISM AND UREA SYNTHESIS: Many factors influence the degradation of dietary proteins in the rumen, post-ruminal protein metabolism and urea synthesis in cattle. Strong positive correlations between nitrogenous fertiliser use and the crude protein content of pastures were identified by use of meta-analysis. Similar strong positive correlations were noted between dietary protein intake, rumen ammonia and plasma urea concentrations. The costs of urea synthesis include energy losses, and importantly, the loss of endogenous amino acids, which are deaminated in the synthesis of urea. MILK UREA AS AN INDICATOR OF PROTEIN METABOLISM: Urea concentrations in blood, plasma and milk are strongly correlated. Milk is an adequate indicator of blood and plasma urea content, but non-nutritional factors may significantly influence milk urea concentrations. Recommendations for dietary protein management based on milk urea concentrations must be undertaken with care.

Gonadotrophin-releasing hormone in postpartum dairy cattle: a meta-analysis of effects on reproductive efficiency

The efficacy of gonadotrophin-releasing hormone (GnRH) or synthetic analogues in improving the reproductive performance of dairy cows less than 40 days postpartum has not been established. It was postulated that disparity observed between the results of similar trials may have arisen from differences in study design, including the dosage of GnRH used; the number of days after calving at which GnRH was administered; the concurrent use of prostaglandins to induce oestrus; and the enrollment of cows with an abnormal puerperium. The results of 24 trials, extracted from 12 research papers were assessed using meta-analysis. When all trials were considered, treatment with GnRH did not significantly alter the number of days to first oestrus or first service or the relative risk of pregnancy at first service (P > 0.05). While treatment did significantly reduce the number of days open by 2.75 days and the number of services per conception by 0.05 services, the results of these studies were heterogenous (P < 0.001) and the validity of pooled estimates questionable. The results of the subgroup of studies that enrolled only cows with a normal puerperium were homogenous for all outcomes examined (P > 0.43), although none of the pooled estimates were significant. Sensitivity analyses, performed by excluding the consistently outlying results of one study, improved the homogeneity of all outcomes (P > 0.03) and produced a significant reduction of 4.52 days to first oestrus in treated cows. Pooled estimates derived without the results of the outlying study were considered more valid indicators of the direction and likely magnitude of effect than those derived in the heterogenous overall analyses. The results of this meta-analysis showed that while blanket treatment of dairy cows in the postpartum period may reduce the number of days to first oestrus, subsequent reproductive performance is unaltered. The study also demonstrated a need to concentrate further research on the potential for treatment with GnRH during the postpartum period to improve the reproductive performance of cows with an abnormal puerperium.

An evaluation of transovarian uptake of metabolites using arterio-venous difference methods in dairy cattle

Arterio-venous (A-V) difference techniques were used in cattle to examine ovarian energy metabolism, cholesterol uptake and steroid hormone outputs. Catheters were inserted into the ovarian vein and facial artery, and Transonic flow transducers were placed around the ovarian A-V plexus. Further, in some cows, the effects of a challenge with GnRH were examined. Glucose uptake and lactate output were significant in most individual cows. Nonesterified fatty acids (NEFA) uptake were not significant in any cow in dioestrus. Ovarian uptake of beta-Hydroxy-butyrate (3-OHB) was significant in 4 cows in dioestrus. Cholesterol uptake was significant in only 1 cow. Oxygen uptake was significant in all cows at all stages of the oestrous cycle. All cows had significant output of progesterone and oestradiol-17 beta. These data show that the bovine ovary utilises significant amounts of glucose, and Respiratory quotient (RQ) estimates demonstrated that glucose was the primary fuel used by the ovary. The significant output of lactate suggested that anaerobic pathways were mainly used for glucose oxidation. The observed uptakes of 3-OHB indicated that the ovary utilises 3-OHB as a source of energy. Cholesterol uptake was not a rate-limiting factor for steroid hormone production in the ovary. Despite the high metabolic rate in the luteal ovary, the small difference in PO2 between arterial and ovarian venous blood indicated that the ovary consumes only a small proportion of available oxygen. GnRH had no significant effect on the uptake of metabolites and energy metabolism, but it increased OBF and the output of progesterone and oestradiol-17 beta. The use of A-V methods to determine the metabolic needs of the ovary is useful in understanding the means by which nutrition can influence fertility.

Short-term studies of ovarian metabolism in the ewe

The ovarian uptake of metabolites in anaesthetised ewes was determined. In both studies, catheters were inserted into the ovarian vein and femoral artery, and Transonic flow transducers were placed around the ovarian arterio-venous plexus. Arterio-venous differences in glucose, lactate, free fatty acids (FFA), 3-hydroxybutyrate (3-OHB), acetate, cholesterol and progesterone and oestradiol-17 beta levels were determined every 10 min over a 3.5 h period. In study one, glucose uptake was significant in three sheep, and one sheep only had a significant uptake of FFA. Ovarian 3-OHB uptake was significant in two sheep. significant uptake of acetate or cholesterol was identified in one sheep. Progesterone secretion was significant in three sheep and two sheep had significant progesterone uptake. In study 2, glucose uptake was significant in four sheep and lactate release was significant in the same sheep. There was uptake of FFA and 3-OHB, cholesterol, and acetate in each of three different sheep. Oestradiol-17 beta output was significant for sheep in oestrus and prooestrus. While the effects of gonadotrophin-releasing hormone (GnRH) treatment were confounded by time spent under anaesthesia, exogenous GnRH appeared to have no significant effect on the uptake of most metabolites and steroid hormone outputs. The metabolic requirements for energy and precursors for progesterone was small. Glucose was the major source of energy for the ovary and appears to be metabolised through anaerobic pathways, as indicated by significant lactate output.

Effects of monensin on the metabolism of periparturient dairy cows

The effects of monensin on plasma concentrations and changes in plasma concentrations of energy metabolites and minerals over time were investigated using 24 multiparous Holstein cows. Cows were paired according to farm, predicted date of calving, and body condition score and were randomly allocated to two groups. Treated cows were given a ruminal bolus containing 32 g of monensin at 50 +/- 7 d before predicted calving. Treated cows had lower plasma concentrations of glucose, free fatty acid (FFA), and beta-hydroxybutyrate (BHBA) than did control cows before calving, indicating that monensin influenced energy metabolism. However, no significant differences in plasma concentrations of glucose, FFA, and BHBA were found between groups after calving. Plasma BHBA concentrations increased more before calving in control cows, and plasma FFA and urea concentrations increased significantly before calving in all cows. No significant differences in body weight, plasma concentrations of urea, or whole blood concentrations of glutathione peroxidase were detected between groups before or after calving. Plasma ceruloplasmin activity did not differ between groups before calving, but was significantly higher in treated cows after calving. Plasma concentrations of Ca did not significantly differ between groups before or after calving. Monensin altered both energy and mineral metabolism and has the potential to improve the health and production of dairy cows.

A case-control study to identify farm factors affecting fertility of dairy herds: univariate description of factors

OBJECTIVE

To identify farm factors which were associated with reproductive performance in dairy herds in New South Wales.

PROCEDURE

A survey was administered by face to face interview to examine the responses of producers drawn from 757 herds, which used the New South Wales Agriculture Department Dairy Herd Improvement scheme. A case-control approach was used to select a total of 126 herds from the first (top group-cases) and fourth quartiles (low group-controls) for intercalving interval.

RESULTS

We found that the estimated interval from calving to first mating was significantly different between group (P = 0.03) and that the groups significantly differed in both their target for interval to first mating (P = 0.02) and their perceived optimum time for first mating (P = 0.04). Other factors associated with a longer intercalving interval included, use of embryo transfer programs (P = 0.08), younger managers (P = 0.02), fewer breedings per day (P = 0.01), a greater number of people detecting heats (P = 0.07), but less hours spent detecting heats while handling the cows (P = 0.11), and a failure to vaccinate bulls for campylobacteriosis (P = 0.14).

CONCLUSIONS

Managers of herds with poorer reproductive performance did not intend to mate cattle as soon after calving as managers with better reproductive performance, were not as active in seeking veterinary advice on reproduction, and were attempting to treat reproductive diseases and disorders themselves.

A case-control study to identify farm factors affecting fertility of dairy herds: multivariate description of factors

OBJECTIVES

To determine whether a multivariate model could be developed to describe farm factors affecting fertility of dairy herd and to examine the factors that determined better reproductive performance on dairy farms in New South Wales.

PROCEDURE

We examined the results of a survey of breeding practices, mating policies, recording systems, timing of mating, heat detection, treatment of metritis and manager demographics of dairy farms using Principal components analysis, logistic regression and the sign test.

RESULTS

Eight principal components for heat detection computed using Principal component analyses were included in the multivariate model to reflect primary and secondary heat detection signs used in the breeding decisions of managers. A final model identified three variables: optimum number of days to first service, number of people detecting heats, and age of manager which significantly influenced the risk of being in the high or low reproductive performance groups. A failure to breed at an appropriate time after calving and having more people responsible for heat detection was associated with herds with a prolonged intercalving interval. While the model provided a good fit for the data, it was not highly discriminatory. Examination of 83 management practices affecting fertility using the sign test (P = 0.01) indicated that managers of herds with good reproductive performance employed better management and breeding practices more often than managers of herds with poor reproductive performance.

CONCLUSIONS

Mating cows sooner after calving and using fewer people to detect oestrus should reduce calving to conception intervals. Veterinarians investigating herd reproductive performance should consider the potential for a number of subtle failures of management to significantly impair fertility rather than limit investigations to a few factors.

The effects of lactation on the fertility of dairy cows

Lactation has been negatively associated with fertility because pregnancy rates in maiden heifers exceed those obtained after first or subsequent calvings. The extent of this difference is less in pasture-fed dairy cows ( < 10%) than in American Holsteins ( > 20%) fed grain and conserved forages. The latter cows have pregnancy rates to first insemination and oestrus detection rates of only 40 to 45%. This suggests that the subsequent fertility of inherently fertile Holstein heifers may be severely compromised by high levels of milk production. International comparisons show that pasture-fed dairy cows may experience extended periods of anovulatory anoestrum but have normal fertility (60% pregnancy rate to first insemination) once cycling. The high-producing American Holstein may ovulate within 4 weeks postpartum but is more likely to continue ovulating without being detected in oestrus. Both situations are associated with negative energy balances (NEB) during early lactation. The severity and duration of this NEB may vary with body condition at calving, age or parity, ration formulation, production level and environmental factors. Relative daily milk yield is not an absolute indicator of NEB, because some lower producing cows within a herd have lower feed intakes and more severe energy deficits. NEB is not simple to measure; nonetheless, it is correlated with genetic improvement for milk yield. A positive energy balance, greater weight gain and higher body condition score have all been shown to be positively correlated with plasma progesterone concentrations in early lactation. No studies have investigated the possibility that the rapid increase in metabolic rate at this time may also alter steroid concentrations with consequent effects on oestrous behaviour and fertility. Studies to more precisely define the effects of increasing milk yields in early lactation, especially in Holsteins, may need to be completed in Australia and New Zealand. Oestrus detection rates and pregnancy rates for American Holsteins of less than 50% are accepted widely in the USA. Such low detection rates confound studies on fertility. The objective should be to increase these 2 rates to at least 80% and 60% respectively. This may involve the use of controlled breeding, especially if oestrous behaviour is less overt in high-producing Holstein cows.

Investigation by meta-analysis of the effect of prostaglandin F2 alpha administered post partum on the reproductive performance of dairy cattle

The effects of injecting prostaglandin F2 alpha (PGF) in dairy cattle within 40 days of calving on the rate of pregnancy at first service and on the number of days open were investigated by meta-analysis, by pooling data from numerous independent trials into single analyses. A total of 4052 cows from 24 trials described in 10 papers were included in the analyses of first service pregnancy rate and 2646 cows from 21 trials described in nine papers in the analyses of the number of days open. The analyses were stratified by trial and by the reproductive health of the cows after calving. Treatment with PGF during this early post partum period had no significant effect on the first service pregnancy rate of cows with a normal or abnormal puerperium. An analysis of the data for the number of days open by effect-size methods showed that a significant percentage (54 per cent) of the treated cows had fewer days open than the untreated cows, and that this difference tended to be greater for cows with an abnormal puerperium (59 per cent of treated cows). The weighted average reduction in days open between the treated and control cows was 2.6 days for trials with abnormal cows, and 3.3 days for trials including normal and abnormal cows. However, the calculation of the fail-safe number (F) indicated that it would require only a few studies with a negative response to PGF to negate this finding. Meta-analysis was a useful technique for evaluating the apparently conflicting results of previous studies.

Effects of cereal grains on fibre digestion in vitro

Cereal grains including wheat, barley, oats, maize and sorghum were incubated with strained rumen fluid in vitro with either ryegrass or lucerne in the ratios of 0:100, 25:75, 50:50, 75:25 and 100:0 at 3g�C for 24 h. Expected NDF digestibilities in mixtures of cereal grain and forage were calculated by interpolation between NDF digestibilities of each grain and of each forage. These were compared with measured NDF digestibilities to detect deviations due to synergism or inhibition. Wheat, barley and maize had inhibitory effects, whereas oats and sorghum had synergistic effects, on NDF digestibility with both forages.

Bovine ketosis and somatotrophin: risk factors for ketosis and effects of ketosis on health and production

Aspects of the metabolism and health of 63 cows which had been treated with different amounts of bovine somatotrophin (BST) daily in the preceding lactation and 25 control cows were studied. The aims of the study were first, to identify cows with ketotic conditions, either by measurements of blood metabolite concentrations or by clinical observations, secondly, to evaluate the risk of such conditions in cows treated with BST in the preceding lactation, and thirdly, to examine the metabolic and production consequences of the ketotic conditions in an environment in which the cows' health, body condition and nutrition were closely observed. The cows were categorised objectively by the use of cluster analysis into non-ketotic cows and ketonaemic cows, on the basis of their plasma metabolite concentrations. Twelve of the control cows and none of the cows previously treated with BST were classified as ketonaemic. Similarly, nine of the control cows but only two of the cows previously treated with BST had clinical ketosis. Some, but not all, of the decrease in the risk of clinical ketosis was attributable to the lower body condition score of the cows previously treated with BST. The clinically ketotic cows had a greater risk of other illness in the first 10 days post partum than their herdmates, but the ketonaemic cows had a significantly lower risk of other disease in the first 10 days post partum. The ketonaemic control cows were significantly heavier than the non-ketotic control cows, but they maintained a higher dry matter intake than the latter cows, probably a key factor in reducing the risk of clinical ketosis.

Effects of sodium monensin on reproductive performance of dairy cattle. I. Effects on conception rates, calving-to-conception intervals, calving-to-heat and milk production in dairy cows

A total of 1061 lactating dairy cows in six different herds were randomly allocated to treatment and control groups. One herd was lot-fed on total mixed rations; three herds were fed on pasture with significant amounts of supplementary concentrates, and two herds were primarily pasture fed. Treated cows received a slow-release, intraruminal capsule containing 32 g sodium monensin within 7 days of calving. Conception rates at first service, days to first oestrus and calving-to-conception interval did not differ significantly between untreated and monensin-treated cows in the 5 herds, 3 herds and 4 herds, respectively, in which these outcomes were examined. Treatment of lactating cows immediately after calving may not be the optimal method to achieve fertility responses with capsules containing sodium monensin. Monensin treatment significantly increased milk yield in one of the six herds. Milk fat or milk protein production was not significantly affected by treatment.

Effects of sodium monensin on reproductive performance of dairy cattle. II. Effects on metabolites in plasma, resumption of ovarian cyclicity and oestrus in lactating cows

A randomised trial was conducted to determine the effects of sodium monensin on plasma metabolite concentrations, resumption of cyclicity and oestrus and milk production and milk composition of postparturient dairy cows. Cows treated with sodium monensin in a controlled-release capsule had significantly lower plasma beta-hydroxybutyrate (BHB) concentrations (P = 0.006) and tended (P = 0.07) to have significantly higher plasma glucose concentrations than untreated cows. Treatment did not significantly influence plasma free fatty acid, urea nitrogen or cholesterol concentrations. Despite higher plasma glucose concentrations and lower plasma BHB concentrations, periods from calving to first ovulation and oestrus were not reduced by treatment. This observation, with limited numbers of cows, is not consistent with a hypothesis that glucose or ketones are important metabolic regulators of pulsatile release of luteinising hormone and consequent resumption of cyclicity. While milk production and milk protein concentration did not significantly differ between groups, milk fat concentration was significantly lower for treated cows. Treated cows probably had lower dry matter intake than untreated cows as they produced 67 litres less milk per head and lost more weight than untreated cows during the study period, although weight and body condition score were not significantly affected by treatment. The lack of significance of these latter observations probably reflects the low statistical power of the study.

Microbial fermentation of cereal grains in vitro

The stoichiometry of fermentation was investigated in vitro with wheat and maize grains. Gas production proved to be an accurate index of VFA production and change in pH. Gas and total VFA production from wheat were strongly correlated with starch disappearance. On a stoichiometric basis, 66% of gas and 64% of VFAs produced from wheat were accounted for by starch fermentation. With maize only 18% of gas and 23% of VFAs produced were accounted for by starch disappearance. There were significant differences between grain species in rates of gas production (P < 0.001), being ranked in the order wheat > triticale, oats > barley > maize > rice, sorghum. Effects of varieties and growing sites on gas production were significant with wheat, oats, maize and sorghum. With barley, only varietal effects were significant (P < 0.001). With maize and sorghum, there were significant variety by site interactions.

Gonadotrophin-releasing hormone treatment in cattle: a meta-analysis of the effects on conception at the time of insemination

Data from 40 trials described in 27 published papers were analysed by meta-analysis (pooling of data from numerous trials into a single analysis) to evaluate the effects of injecting gonadotrophin-releasing hormone (GnRH) in cattle at the time of insemination on the risk of pregnancy. A total of 19,019 cows were involved in these studies. Analyses were stratified by trial and by the effects of dose of GnRH, type of GnRH and insemination number (first, second or third and greater). Mantel-Haenszel analysis revealed that use of GnRH at insemination significantly increased the overall risk of pregnancy by 12.5% in treated cows (P < 0.05). However, increases in risk of pregnancy were greatest (22.5%) when repeat breeders were tested. Results for use of GnRH or analogue at first service were similar, with increased risks of pregnancy in treated cows of 5.2 and 8.0%, respectively. The risk of pregnancy tended to be higher (11.1%) when the dose of GnRH was > or = 250 micrograms and when used at second insemination (9.9%). The analyses demonstrated that while treatment at insemination with GnRH and GnRH analogues increased conception rates in dairy cattle, some variation in study results was attributable to the number of inseminations after calving at which GnRH is administered. Further efforts should be made to determine characteristics of populations of cows that have good fertility responses to GnRH and to determine the mode of action of GnRH in increasing fertility.(ABSTRACT TRUNCATED AT 250 WORDS)

Within and between observer agreement on ultrasonic evaluation of bovine ovarian structures

A diagnostic ultrasound unit with a 5 MHz probe was used to examine ovarian structures in vitro from 32 reproductive tracts obtained at slaughter from young cows. Agreement between and within observers, and between observers and dissection results was evaluated using the kappa statistic. Agreement was high (kappa from 0.531 to 0.969) for all evaluations of corpora lutea. The sensitivity, specificity and predictive value of both positive and negative findings for presence of a corpus luteum was > 0.9. Agreement between and within observers was little better than chance for follicles measuring 4 to < 6 mm and for follicles measuring 6 to < 10 mm. However, agreement between observers and dissection results indicated that observers could detect follicles 4 to < 6 mm and 6 to < 10 mm (kappa 0.301 to 0.731 and 0.414 to 0.612, respectively). Kappa values within and between observers and between observers and dissection results for observations of follicles measuring > or = 10 mm were almost all > 0.4 indicating that large follicles can be readily detected using ultrasound. It is suggested that further validation of ultrasound methods is needed to determine whether follicles measuring < 4 mm can be accurately identified, and whether follicles can be accurately identified and monitored over a number of days. The ultrasound unit was useful for detecting the presence of corpora lutea and follicles. However, agreement between and within observers on the presence of follicles measuring < 10 mm was poor.

Time series cross-correlation analysis of postparturient relationships among serum metabolites and yield variables in Holstein cows

Time series cross-correlation analysis was used to determine relationships among serum beta-hydroxybutyrate, glucose, FFA, cholesterol, milk yield, DMI, and estimated net energy balance for 42 d postpartum for 14 multiparous cows. Milk yield was positively associated with beta-hydroxybutyrate concentrations on the same day, and milk yield was a primary determinant of metabolic change. Dry matter intake was negatively correlated with beta-hydroxybutyrate concentrations 3 d later and on the same day. The data supported in vitro studies showing that FFA are positively associated with beta-hydroxybutyrate production, showed that glucose concentrations are negatively cross-correlated with beta-hydroxybutyrate concentrations, and found that estimated net energy balance is negatively cross-correlated with beta-hydroxybutyrate. Analyses suggested that serum glucose and cholesterol concentrations significantly decreased with increased milk yield; analyses also suggested that elevated beta-hydroxybutyrate concentrations were associated with decreases in milk yield 6 d later. beta-Hydroxybutyrate and FFA concentrations 3 to 9 d before parturition were positively related to cholesterol concentrations, and relationships were positive between estimated net energy balance and cholesterol, suggesting that cholesterol concentrations increased as precursors for cholesterol synthesis were available. Time series cross-correlation analysis was a useful tool in examining relationships among variables when repeated samples were obtained from the same individuals.

Impact of bovine somatotropin administration beginning at day 70 of lactation on serum metabolites, milk constituents, and production in cows previously exposed to exogenous somatotropin

Metabolic and production responses are reported for 72 cows treated with bovine somatotropin (BST) for 30 days starting at day 70 of lactation. Of these 72 cows, 48 had been exposed in the preceding lactation to long-term treatment with BST at 3 dosages and 24 (controls) had not been given BST. Approximately half of the cows in each group were parity-2 cows, the rest were older. Comparisons between groups were made separately for parity-2, and older cows. Analyses, using pretreatment values of each variable as a covariate, indicated that older cows, but not parity-2 cows, significantly (P less than 0.05) increased milk production during treatment. Parity-2 cows, however, had a significantly higher milk fat percentage than controls following treatment. Cows treated with 51.6 or 86 mg BST/d in both parity groups had significantly higher serum-free fatty acids than controls. Estimated net energy balances were significantly lower for older treated cows, but did not significantly differ from controls for parity-2 treated cows. Older cows in the 86 mg of BST/d group tended to have higher concentrations of blood glucose than did older control-group cows. Treatment with BST did not significantly increase serum ketone concentrations in any group of animals, and none of the cows developed clinical ketosis during this period. Estimated net energy balance (ENEB) during treatment was a significant (P less than 0.05) covariate for free fatty acid concentrations in older cows and for milk fat percentage in parity-2 cows. Covariate adjusted analyses, using ENEB during treatment as a covariate, indicated that lipolytic stimuli already acting may be enhanced by treatment with BST, but a negative energy balance was not a necessary precondition for free fatty acid concentrations to increase following somatotropin treatment. Similarly, milk fat percentages for parity-2 treated cows were significantly (P less than 0.05) higher during treatment than controls when ENEB during treatment was used as a covariate. Increased milk fat concentrations in parity-2 treated cows were not associated with significant increases in the ratio of C18:C4-10 milk fatty acids, indicating that increased milk fat resulted from either an increase in incorporation of C18 fatty acids into milk fat coupled with an increase in de novo mammary synthesis of C4-10 milk fatty acids or an increase in C12-16 fatty acids that may arise either from increased tissue mobilization, from diet, or from de novo mammary synthesis.

Bovine somatotropin

Bovine somatotropin has the potential to alter profoundly the way that dairy herds are managed and to change the ways in which veterinarians provide services to those herds. This article describes the structure, function, and action of somatotropin. The metabolic effects of somatotropin on dairy cattle are discussed.

Postparturient metabolic and production responses in cows previously exposed to long-term treatment with somatotropin

Postparturient metabolic and production responses were studied for 85 multiparous cows consisting of controls and animals that had been previously exposed to long-term treatment with bST. Older cows previously exposed to bST at high doses (51.6 mg/d) had lower milk yields than controls. However, there were no significant differences compared with controls in milk yield for lower dose (17.2 mg/d) older cows or parity 2 cow groups. The bST-treated groups had higher postpartum DMI, lower serum FFA, lower serum beta-hydroxybutyrate levels, and higher serum glucose than controls. Some bST-exposed groups had lower milk fat but higher milk protein levels. All bST-treated groups had significantly lower ratios of C18 to C4 to 10 milk fatty acids. Control cows of both parity groups were in higher body condition and weighed more than bST-treated cows prior to calving. The differences in postpartum metabolism may be attributed to differences in body composition resulting from bST treatment in the prior lactation, because use of body condition score prior to calving as a covariate did not substantially alter responses. The control cows probably had greater reserves of mobilizable lipid. These contentions are supported by changes in milk composition for bST-treated cows, which were consistent with animals of greater appetite, mobilizing less lipid. The bST-treated cows were probably more energetically efficient milk producers because they produced milk from feed rather than from mobilization of tissue stores. These data suggest that bST use in a prior lactation may have potential benefit in reducing risk of metabolic disorders associated with lipid mobilization in the postparturient period.

An investigation of bulk tank milk selenium levels in the San Joaquin Valley of California

We evaluated selenium determination of bulk milk tank samples as an alternative to testing blood selenium for evaluating herd selenium status in DHIA dairy herds in the San Joaquin Valley of California. A method of determining milk selenium levels using inductively coupled plasma spectrometry is described. Mean bulk tank milk selenium levels were 0.0224 mg/L (Range 0.0126-0.0418 mg/L). No statistically significant relationships were found between bulk tank milk selenium levels of a herd and calving interval, days open or log somatic cell counts. Mean herd blood and milk levels were directly proportional to bulk tank milk selenium levels. Within a herd milk selenium levels of a cow were directly proportional to the cow's blood selenium level. Herd selenium levels were not significantly related to soil selenium levels. Determination of bulk tank milk selenium levels has the potential to be a low cost, non-invasive means of evaluating herd selenium levels in order to determine selenium deficiency. Further studies with this technique in areas which are deficient in selenium may provide estimates of the sensitivity, specificity and predictive value of bulk milk tank selenium for determining selenium deficiency in dairy herds.

Tryptamine alkaloid toxicosis in feedlot sheep

Tryptamine alkaloid toxicosis (Phalaris staggers) was diagnosed in feedlot sheep. Clinical signs of toxicosis, which were exacerbated by excitement, included gait abnormalities, muscular tremors, nystagmus, and convulsions. An estimated 8% of the most severely affected lambs had clinical signs of toxicosis. Gross lesions detected in the brain of affected lambs consisted of focal gray-green discoloration in the brain stem and thalamus; these areas had microscopic evidence of intraneuronal pigment accumulation. Brain specimens obtained at slaughter indicated that 60% of the lambs had lesions consistent with tryptamine alkaloid toxicosis. Tryptamine alkaloids were found in low concentrations in the feed. Lambs exposed to these feeds had higher death losses than those that were not exposed to the feeds. Cobalt concentration in the feed was higher than that previously reported to be associated with Phalaris staggers.

Relationships between fertility, peak milk yields and lactational persistency in dairy cows

Peak milk yield, lactational persistency and conception rates were studied using 5928 lactation records of high milk-producing cows at three California dairies. Log-linear analysis was used to study relationships between peak milk yield, lactational persistency, dairy of origin, lactation number and conception rates in 3850 completed lactations. Cows with peak milk yields greater than the median (38.2 kg milk per day) were less likely to have conceived in one or two breedings than cows with peak milk yields lower than or equal to the median. Cows with a higher than median (0.755) lactational persistency were less likely to have conceived in one or two breedings than cows with a lactational persistency lower than or equal to the median. Dairy of origin had a significant effect on the probability of conceiving in one or two breedings. Cows in the first lactation were more likely than those in subsequent lactations to conceive in one or two breedings. This retrospective study demonstrated that subfertility is associated with high peak lactational yields in high milk-producing California cows.

Corynebacterium pyogenes mastitis outbreak in inbred heifers in a California dairy

An outbreak of Corynebacterium pyogenes mastitis ("Summer Mastitis") was observed in a group of 96 heifers. The outbreak affected 8 animals, of which 7 were too young for breeding. The disease incidence was highest in calves 2 to 4 months old. Cases were observed over an initial estimated 14 day period with a further case being detected 14 days subsequently. Corynebacterium pyogenes mastitis has not been reported in calves this age. Factors postulated to influence the outbreak include the presence of large numbers of flies, intersucking of calves, and possible viral disease.