The role of nutrition and photoperiod in the timing of puberty

Photoperiod Impacts Nucleus Accumbens Dopamine Dynamics

Circadian photoperiod, or day length, changes with the seasons and influences behavior to allow animals to adapt to their environment. Photoperiod is also associated with seasonal rhythms of affective state, as evidenced by seasonality of several neuropsychiatric disorders. Interestingly, seasonality tends to be more prevalent in women for affective disorders such as major depressive disorder and bipolar disorder (BD). However, the underlying neurobiological processes contributing to sex-linked seasonality of affective behaviors are largely unknown. Mesolimbic dopamine input to the nucleus accumbens (NAc) contributes to the regulation of affective state and behaviors. Additionally, sex differences in the mesolimbic dopamine pathway are well established. Therefore, we hypothesize that photoperiod may drive differential modulation of NAc dopamine in males and females. Here, we used fast-scan cyclic voltammetry (FSCV) to explore whether photoperiod can modulate subsecond dopamine signaling dynamics in the NAc core of male and female mice raised in seasonally relevant photoperiods. We found that photoperiod modulates dopamine signaling in the NAc core, and that this effect is sex-specific to females. Both release and uptake of dopamine were enhanced in the NAc core of female mice raised in long, summer-like photoperiods, whereas we did not find photoperiodic effects on NAc core dopamine in males. These findings uncover a potential neural circuit basis for sex-linked seasonality in affective behaviors.

Effect of biostimulation on growth rate and reproductive development of Bos indicus dairy heifers

The present study aimed to compare the growth rate, feeding behavior, reproductive development, and concentrations of GH and leptin in Sahiwal heifers exposed to direct bull contact, bull contact through a fenceline, or isolated from bulls. Overall, 24 heifers were allotted to three treatment groups (n = eight/group) based on birth weight, body weight, and age. Heifers from the non-exposed group (NBE) remained isolated from bulls; heifers stimulated by fenceline bull contact (FBE) remained continuously exposed to bulls through a fenceline, and heifers with direct bull contact (DBE+FBE) had direct contact with a bull during 6 h/day plus continuous fenceline bull exposure for the entire 24 h period. It was considered that heifers attained puberty when progesterone concentration was >1 ng/mL. Biostimulated heifers achieved puberty at both a lower age and body weight (P < 0.05) than NBE heifers. Overall, average daily gain (g/day) was greater in DBE+FBE (516.3 ± 4.5) and FBE (501.6 ± 4.3) than in NBE (441.8 ± 2.9, respectively; P < 0.01). Leptin and growth hormone concentrations were significantly greater in FBE and DBE+FBE than NBE heifers. Both groups of biostimulated heifers devoted more time eating than NBE heifers, P < 0.05). In conclusion, biostimulation of Sahiwal heifers, either by exposing them to bulls through a fenceline or by both fenceline exposure and direct contact, reduced the age of puberty and increased growth performance. Overall, fenceline bull exposure can be recommended as an easy handling management to stimulate reproductive precocity and growth rate in heifers.

Genome-scan analysis for genetic mapping of quantitative trait loci underlying birth weight and onset of puberty in doe kids (Capra hircus)

The objective of this study was to locate quantitative trait loci (QTL) causing variation in birth weight and age of puberty of doe kids in a population of Rayini cashmere goats. Four hundred and thirty kids from five half-sib families were genotyped for 116 microsatellite markers located on the caprine autosomes. The traits recorded were birth weight of the male and female kids, body weight at puberty, average daily gain from birth to age of puberty and age at puberty of the doe kids. QTL analysis was conducted using the least squares interval mapping approach. Linkage analysis indicated significant QTL for birth weight on Capra hircus chromosomes (CHI) 4, 5, 6, 18 and 21. Five QTL located on CHI 5, 14 and 29 were associated with age at puberty. Across-family analysis revealed evidence for overlapping QTL affecting birth weight (78 cM), body weight at puberty (72 cM), average daily gain from birth to age of puberty (72 cM) and age at puberty (76 cM) on CHI 5 and overlapping QTL controlling body weight at puberty and age at puberty on CHI 14 at 18-19 cM. The proportion of the phenotypic variance explained by the detected QTL ranged between 7.9% and 14.4%. Confirming some of the previously reported results for birth weight and growth QTL in goats, this study identified more QTL for these traits and is the first report of QTL for onset of puberty in doe kids.

Effect of nutritional growth restriction on timing of reproductive development and plasma concentrations of insulin-like growth factor-1 and growth hormone in male red deer (Cervus elaphus) reared in constant photoperiod

The effect of nutritional growth restriction on reproductive development in red deer stags reared in constant photoperiod was investigated and the correlation between reproductive status and circulating concentrations of growth hormone (GH) and insulin-like growth factor-1 (IGF-1) examined.

Stags were reared from birth in constant photoperiod (12 h light: 12 h dark). They were offered a ‘complete diet’ ad libitum until they reached 52-5 kg live weight (LW) and were then maintained at this LWby restricting daily food dry-matter intake (DMI)for either a long (LR, 26 to 51 weeks of age, no. = 5) or short (SR, 21 to 33 weeks, no. = 6) period before being returned to ad libitum feeding.

Relative to SR stags, antlers hardened later in LR stags (72·0 v. 57·5 weeks of age, P < 0·001); sustained elevations in plasma testosterone also began later (55·2 v. 38·5 weeks, P < 0·001) but at lower LW (54·0 v. 60·6 kg, P < 0·05). In both groups, the testosterone rise followed the return to ad libitum food by 4 to 5 weeks. Plasma IGF-1 was closely correlated with DMI (LR, r = 0·84, P < 0·001; SR, r = 0-93, P < 0·001) and with plasma testosterone (LR, r = 0·42, P < 0·001; SR, r = 0·38, P < 0·01). Also the increase in plasma IGF-1 preceded that of testosterone (by 2·8 (s.e. 0·94) weeks) and was associated with a transient plasma GH peak (P < 0·05) and elevated LH concentrations (SR, P < 0·01; LR, P < 0·05).

The timing of reproductive development in growth-restricted male red deer in constant photoperiod may therefore be more sensitive to DMI than LW, and changes in plasma IGF-1 concentrations are consistent with a putative permissive role in relaying this information.

The effects of early environmental conditions on the reproductive and somatic development of juvenile guinea pigs (Cavia aperea f. porcellus)

Little is known about the effects of the early environment on the development of non-seasonally reproducing species like the domestic guinea pig (Cavia aperea f. porcellus). Although guinea pigs reproduce throughout the year, there is evidence for environmental sensitivity of their reproductive physiology. To investigate the sensitivity of juvenile body weight and puberty to differences in the prenatal and early postnatal environment, subjects were exposed to either of two experimental conditions mimicking seasonal variation: a long photoperiod with 25 degrees C ambient temperature ("LD/25 degrees C"), or a short photoperiod with 15 degrees C ("SD/15 degrees C"). Mean body weight of F1-males from LD/25 degrees C-conditions was higher than that of SD/15 degrees C-males during the whole pubertal period, although the difference was significant only during the early growth phase. Testosterone concentrations also differed significantly between the two treatment groups, pointing to an earlier pubertal onset in LD/25 degrees C- than SD/15 degrees C-males. In F1-females, treatment effects on body weight or age at first estrus were absent. This indicates that the somatic and reproductive development is more sensitive to early photoperiod and temperature conditions in male than female guinea pigs, and that other environmental factors may also play a crucial role for reproductive maturation in this species.

Comparison of feed preference and digestion of three different commercial diets for cats and ferrets

Diet preference and digestibility experiments were conducted using a total of 10 cats and 10 ferrets. The composition of the three different kinds of dry cat feed was as follows (each data are given in dry matter, DM): (i) normal diet (N): 95.3% DM, 33.7% crude protein (CP), 20.4% ether extract (EE), 37.6% nitrogen-free extract (NFE); (ii) 'light diet' (L): 94.2% DM, 31.6% CP, 10.7% EE, 52.2% NFE; (iii) 'veterinary diet' (D): 94.57% DM, 38.7% CP, 9.6% EE, 47.2% NFE. During the period of the preference test, the average daily dry matter intake (calculated with the mean of the three diets: 94.7% DM) was 98.0, 15.0 and 16.7 g DM in cats and 25.0, 7.3 and 8.1 g DM in ferrets. The preference rates of the three different diets, expressed in percentage of their total consumption, were as follows: 60.4% N (54.4 g DM), 12.4% L (12.1 g DM) and 27.2% D (26.6 g DM) in cats, and 46.2% N (11.6 g DM), 29.9% L (7.5 g DM) and 23.9% D (6.0 g DM) in ferrets. This indicates that cats and ferrets have a clear preference for diets of higher fat content. In all three diets, the digestibility of CP was significantly (p < 0.05) lower (70.1 +/- 5.4 vs. 75.9 +/- 5.8) while that of EE was significantly (p < 0.05) higher (95.6 +/- 1.5 vs. 89.4 +/- 5.3) in ferrets than in cats. The average digestible/metabolizable energy (DE/ME) ratio of feeds turned to be 95.6% for cats and 90.6% for the ferrets. From the data one can conclude that the ferret cannot be used as a model animal for cats either for preference or digestibility studies.

Onset of puberty in pasture-raised Thoroughbreds born in southern hemisphere spring and autumn

REASONS FOR PERFORMING STUDY

There is little information on age, weight and time of year of puberty in Thoroughbred horses, and the interpretation of such data is difficult due to the wide variety of descriptions of the onset of puberty.

OBJECTIVES

To examine the age, bodyweight and date of onset of puberty in Thoroughbreds born in spring and autumn.

METHODS

Bodyweight data and blood samples were collected in 59 pasture-raised Thoroughbred horses. Five autumn-born and 18 spring-born colts and 3 autumn-born and 33 spring-born fillies were examined from birth to age 13 and 17 months. A testosterone concentration >2 s.d. above the baseline concentration was indicative of onset of puberty in colts; and progesterone concentration >2 ng/ml and at least 3 times greater than the previous progesterone concentration was indicative of a first ovulation in fillies.

RESULTS

Spring-born fillies and colts were older and heavier than autumn-born fillies and colts at puberty. The age at onset of puberty in spring- and autumn-born foals was 291-408 days and 212-270 days, respectively. The weight at puberty in spring-born foals was 302-409 kg, and in autumn-born foals was 277-344 kg. However, the mean date at onset of puberty was not significantly different between spring- and autumn-born horses, with puberty occurring in October (New Zealand spring).

CONCLUSIONS AND POTENTIAL RELEVANCE

Seasonal changes in photoperiod affect the timing of onset of puberty, provided a minimum threshold bodyweight has been reached. Spring-born horses reached this threshold weight during the winter months and remained reproductively inactive until after the stimulus of increasing day-length occurred. The autumn-born horses reached the threshold weight to support puberty at the same time as stimulatory photoperiod and, therefore, reached puberty significantly younger and lighter than the spring-born horses.

Influence of feeding intensity on the growth, body composition and sexual maturity of male New Zealand White rabbits

An experiment was carried out with young male New Zealand White (NZW) rabbits to establish live body weight changes, body measurements, body composition and sexual maturity as a function of feeding intensity. Animals in Group 1 ('AL', n = 10) were fed ad libitum, while those in Group 2 ('RS', n = 10) received restricted feeding corresponding to 70% of the ad libitum level. The starting liveweights were practically the same (0.907 +/- 0.146 and 0.911 +/- 0.147 kg in Group AL and Group RS, respectively). The feeding trial lasted from 6 to 22 weeks of age. The average body weight was significantly higher in Group AL from 7 to 22 weeks of age. At 22 weeks of age the body weight of RS rabbits was 85.64% of the weight of AL animals (3.22 +/- 0.52 kg and 3.76 +/- 0.33 kg, respectively). Average body weights of RS males at 8, 9, 11, 19 and 21 weeks of age were similar to those of ad libitum fed (AL) animals at 7, 8, 10, 15 and 16 weeks of age, respectively. The growth of bucks fed restricted tended to be allometric. The most significant difference was found at 16 and 18 weeks of age, while the lowest difference occurred at 6, 12, 15 and 19 weeks of age. It can be stated that low-intensity feeding up to slaughtering weight causes backwardness in rear cannon length and this backwardness remains also after the 15th week, which is well over the optimal slaughtering age. Based on the present data, the 70% restricted feeding cannot be recommended either for the future breeding bucks or for broiler males reared for slaughter. To determine the major chemical components of the body, rabbits were euthanised. Original dry matter and crude fat content of the body significantly (P < 0.05) decreased under restricted feeding (41.42%; 32.48% and 16.73%; 7.35%) while the percentage of protein within the dry matter increased (49.6%; 65.0%) and fat decreased (40.17%; 22.1%) significantly. Libido unambiguously decreases as a consequence of feed deprivation. The most conspicuous difference was found in the level of blood testosterone. Although a few RS bucks produced semen but only much later than the rabbits fed ad libitum. On the other hand, there was no difference in the motility of spermatozoa and ejaculate volume in comparison with AL animals. There was no relationship between the body fat content and the reproductive status of bucks in the present trial.

Effects of short-term high carbohydrate or fat intakes on leptin, growth hormone and luteinizing hormone secretions in prepubertal fat-tailed Tuj lambs

The aim of the current study was to evaluate the effects of high carbohydrate or fat diets, fed for 15 days at the end of breeding season, on leptin, GH and LH secretions in prepubertal fat-tailed Tuj lambs. For that purpose, 9-month-old ram-lambs were divided into three groups as control group (fed with basal ration, n = 4), high carbohydrate (HC) group, basal ration plus barley, n = 4), or high fat (HF) group (basal ration plus by-pass fat, n = 4). For the measurement of leptin and GH, blood plasma samples were collected on days 1, 4, 9 and 14 of the experiment. For the measurement of LH pulse frequency, serial blood samples were collected every 15 min for 6 h on day 14. Lambs were weighed and body condition scored (BCS) on days 1 and 15. Body weight and BCS increased towards the end of the study (p < 0.05). The BCS was higher in high energy groups at the end of the experiment (p < 0.05). Diet affected plasma leptin concentrations (p = 0.002) but time did not. The GH concentrations were not affected by diet or time. The LH pulse frequency appeared to be higher in HC and HF groups but there were no statistical difference between the groups. There was a significant positive relationship between overall BCS and corresponding leptin concentrations (R2 = 0.263; p = 0.010) and between LH pulse frequency and leptin concentrations (R2 = 0.594; p = 0.003). In conclusion, the present study suggests that rather than type of energy, amount of energy intake and body energy reserves are much important regulators of plasma leptin concentrations and LH pulse frequency in fat-tailed Tuj lambs.

Energy level in winter diets of Fallow deer: effect on plasma levels of insulin-like growth factor-I and sex ratio of their offspring

To determine the effect of dietary energy level in the first winter on subsequent puberty onset, pregnancy, growth, and secretion of progesterone and insulin-like growth factor-I (IGF-I) in Fallow deer, prepubertal deer were fed either a high (H) or a low (L) energy diet in a randomised complete block design. June-born female Fallow deer were fed ad libitum either 12.5MJ/kg DM (H, n=29) or 10MJ/kg DM (L, n=29) in pelleted rations once per day during the winter (approximately 4-10 months of age) preceding puberty. Blood samples were collected twice weekly during the peripubertal period. During the winter feeding period, DM intake was similar for both groups but average daily gain was greater (P<0.05) for deer fed the H versus L diet. Onset of puberty was not affected (P>0.10) by dietary treatment. Concentrations of progesterone in plasma did not differ (P>0.10) between dietary treatments before or after puberty, increasing after puberty in both groups, and reaching maximal levels 8-12 days after the onset of puberty. Concentrations of plasma IGF-I increased (P<0.05) before puberty in both groups reaching maximal levels 3-4 days before the onset of puberty but did not differ (P>0.10) between H and L diets before or after puberty. Of the 28 does fed the H diet that calved, 75% of the calves born were male versus 46% in the L diet (P<0.05). In conclusion, increased plasma IGF-I concentrations were associated with the onset of puberty in Fallow deer regardless of the level of dietary energy intake during the preceding winter. Increased dietary energy during winter does not alter pregnancy rates but does alter sex ratio of calves born.

The missing politics and unsettled science of the trend toward earlier puberty

The age of puberty in many populations has declined steeply over recent centuries and may be declining still. Consequently, today's children tend to experience the hormonal stresses of rapid development at younger ages than did their ancestors, around whose later, if not more gradual, maturation traditional behavioral expectations formed. Little has been made of this "rush to puberty" outside the life sciences. This article reviews its historical documentation, scholarly appreciation, epidemiological correlations, putative physiological and environmental explanations, sociological implications, and largely latent politics.

Effects of diet and injection of bovine somatotropin on prepubertal growth and first-lactation milk yields of Holstein cows

To determine effects of rapid prepubertal growth on first-lactation milk production, Holstein heifers were randomly assigned to one of three treatments. Thirty-five heifers were fed a standard diet to meet NRC recommendations and produce 0.8 kg of body weight (BW) gain/d (standard). Thirty-five heifers were fed a diet with higher energy (2.8 Mcal of metabolizable energy/kg) and protein (19.7% crude protein; high diet) to produce 1.2 kg of BW gain/d (high). Thirty-five heifers were fed the high diet and injected daily with bovine somatotropin (bST) (25 microg/kg of BW; high-bST). Diets were fed and bST was injected from 135 kg of BW until pregnancy was confirmed. Heifers were inseminated after BW exceeded 363 kg. Pregnant heifers were commingled and fed similar diets through gestation, parturition, and lactation. High and high-bST heifers had greater prebreeding average BW gains than standard heifers. Conversely, standard heifers had a greater average BW gain during gestation than high and high-bST heifers. High and high-bST heifers were approximately 90 d younger than standard heifers at first insemination and first parturition. Postpartum BW, body condition scores, and withers heights at parturition, and calving ease scores were not different among treatments. Standard heifers produced 14% more milk than high heifers but not more than high-bST heifers. The high-protein, high-energy diet decreased age at first parturition and first-lactation milk production, but did not affect reproduction. Injection of bST during the prepubertal growth period combined with the high diet decreased age at first parturition without reducing milk production.

Effects of photointensity and photoperiod on milk yield and reproductive performance of Norwegian red cattle

Relationships between light exposure, milk yield, and reproductive traits in Norwegian Red cattle were studied using data from 1538 farms in southern Norway during the darkest part of the year (November 1 to February 28). Production level was expressed as milk yield at first artificial insemination (AI) and 305-d milk yield. Reproductive performance was calculated using the following dependent variables: age at first AI, age at first calving, days open, calving interval, number of AI per cow, and nonreturn rate at 60 d. Days open and calving interval were both 4.0 d shorter, number of AI per cow was 0.07 less, non-return rate was 3.1% greater, and daily milk yield at first AI was 0.5 kg greater in herds that used dim illumination at night compared with herds that used no illumination at night. Milk yield at first AI was 0.5 kg greater in herds with photoperiods > 12 h. Photoperiods > 12 h were associated with a reduction in age at first AI by 4.8 d and age at first calving by 6.6 d. We concluded that dairy cattle kept at high latitudes during winter should be exposed to dim illumination at night and a minimum photoperiod of 12 h to stimulate reproductive performance and milk yield.

Latitude-related changes in the amplitude of annual mortality rhythm. The biological equator in man

There is extensive literature describing the effect of season on mortality rates, especially in cardiovascular and respiratory disease. This study compares latitude with the extent of seasonal variation of monthly deaths from all causes. In developed countries, there is a peak of deaths in winter and a trough in summer. Monthly numbers of deaths were established in 89 countries in the Northern and Southern Hemisphere. Using cosinor analysis, the extent of seasonal variation (amplitude) was established and correlated with latitude. The amplitude of seasonality was greatest in mid-latitude around 35 degrees, but low or absent near the equator and subpolar regions. The amplitude can differ at the same latitude. The weather in equatorial regions and in habitations near the Arctic Circle is very different, but death has a similar seasonal rhythm. The purpose is to record this epidemiological finding even though no simple explanation is provided. Weather alone cannot explain it, and it is possible that day length (photoperiod) has an important, but complex, underlying role.

Effects of diet and bovine somatotropin on heifer growth and mammary development

Forty Holstein heifers [body weight (BW) = 126 kg] were blocked by BW into groups of 4, and, within each block, heifers were randomly assigned to one of four treatments. Twenty heifers had ad libitum access to a diet formulated to produce a BW gain of 0.8 kg/d (control diet), and 20 heifers had ad libitum access to a diet formulated to produce a BW gain of 1.2 kg/d. (high diet). Half of the heifers fed each diet were injected daily with bovine somatotropin (bST; 25 micrograms/ kg of BW). The high diet increased daily BW gain as well as body condition score. Injection of bST also increased daily BW gain, but did not affect body condition score. The high diet reduced age at puberty by 58 d, but did not affect BW, withers height at puberty, or pelvic area at slaughter. Injection of bST had no effect on age at puberty, but increased BW, withers height at puberty, and pelvic area at slaughter. The high diet did not affect mammary parenchymal DNA, RNA, or the ratio of RNA to DNA. The injection of bST increased mammary parenchymal DNA, RNA, and the ratio of RNA to DNA. The high diet was more cost effective for rearing dairy heifers from 120 d of age to potential breeding size (> or = 363 kg of BW and postpubertal) than was the control diet. In conclusion, the high protein, high energy diet increased growth rate without detrimental effects on mammary development. Injection of bST increased BW, skeletal size, and mammary development.

Effect of season of birth on milk, fat, and protein production of Israeli Holsteins

The effects of birth month on production of milk, fat, and protein and percentages of fat and protein were analyzed based on production records of 101,653 first parity, 77,541 second parity, and 51,856 third parity Israeli Holstein cows. Each parity was analyzed separately. The analysis model also included the effects of herd-year, DIM, calving age, and calving month. First parity Type III sums of squares for birth month were nearly as large as those for calving month but decreased for later parities. Similar results were obtained using multiplicative models in which the dependent variables were the logarithms of the production traits. The effects of calving month and birth month were not similar, but birth month had similar effects for milk, fat, and protein production. Production was lowest by cows born in the early spring and highest by cows born in the fall. Analyses of the log-transformed traits showed that the F values for calving month were greater than, and the F values for birth month were nearly identical to, the F values for the untransformed trait analyses. The physiological basis for these trends was not clear.