Effect of plane of nutrition on seasonality of reproduction in Spanish Payoya goats

The aim of this study was to determine if there is a seasonal pattern of sexual activity in female Payoya goats and if this seasonality could be modulated by nutrition. During the experimental period of 20 months, 43 non-pregnant adults goats were penned under natural photoperiod at latitude 37 degrees 15'N. At the onset of the experiment, the animals were allocated to three experimental groups differing in the level of nutrition and whether the animals were entire or ovariectomized does. The high nutrition group (H, n = 16 entire does) receiving 1.5 times maintenance requirements. The low nutrition group (L, n = 16 entire does) and an ovariectomized and oestradiol treated group (OVX, n = 11 ovariectomized does) received a diet supporting their maintenance requirements. The groups were balanced for live weight (LW) and body condition score (BCS) at the beginning of the study. In entire goats, oestrus was tested daily using aproned males, ovulation rate was assessed by laparoscopy 7 days after identification of oestrus and plasma samples were obtained twice per week for progesterone assay. OVX goats were isolated from the other groups and bucks, plasma samples were assayed twice per week for LH and there were four intensive sampling periods during the year to determine LH pulsatility. LW and BCS were recorded for all animals once a week. A clear circannual cycle in live weight change was observed in all experimental groups, being relatively stable or slightly decreasing in summer and autumn and increasing during winter and spring. The effect of exposure to high (H) rather than low (L) nutrition was to cause earlier onset of ovarian activity (5 versus 17 August; P < 0.05), and expression of oestrous (16 August versus 2 September; P < 0.01) and later cessation of reproductive activity (ovulation 11 February versus 17 January; P < 0.01). Consequently, seasonal anoestrus was 32 days shorter in does on the higher plane of nutrition (P < 0.01). The seasonality of reproductive activity was confirmed in the OVX does, with reduced LH concentrations during spring and summer, and increased LH concentrations in autumn and winter. There was no effect of nutrition on ovulation rate. These results demonstrate that the female Payoya goat exhibits marked reproductive seasonality which is modulated by nutrition but possibly not ovulation rate.     

Reproductive performance of heifers induced to oestrous asynchrony by suprabasal plasma progesterone levels

Suprabasal progesterone concentrations around oestrus have induced disturbances in oestrous behaviour and ovulation. To determine whether fertility in such an altered oestrus can be maintained at normal levels with additional inseminations (AI) until ovulation, fertility was compared in heifers (n = 11) inseminated in normal oestrous cycles and thereafter in cycles in which the animals were treated with progesterone in order to create suprabasal concentrations after luteolysis. The treatment consisted of silicone implants containing 10.6 mg kg⁻¹ of progesterone inserted subcutaneously on Day 8 of the oestrous cycle (day of ovulation designated Day 0) and removed on Day 25. Both in control oestrous cycles and oestrous cycles under progesterone treatment, growth of the ovulatory follicle and ovulation were determined by frequent ultrasound scanning. Blood was collected frequently for further analysis of progesterone, oestradiol-17β and luteinising hormone (LH). Insemination was performed 12 h after onset of standing oestrus. if ovulation did not occur 24 h after AI, heifers were inseminated again until ovulation. Pregnancy was diagnosed by ultrasound 25 days after ovulation.In control oestrous cycles, plasma progesterone decreased to 0.3 ± 0.3 nmol 1⁻¹. Duration of oestrus was 22.9 ± 2.0 h, the interval from onset of oestrus to ovulation was 32.4 ± 2.3 h and the interval from LH peak to ovulation was 28.6 ± 1.4 h. The interovulatory interval was 20.7 ± 0.6 days. In oestrous cycles in treated heifers, progesterone decreased to 1.0 ± 0.3 nmol l⁻¹ (P > 0.10) and the interovulatory interval was prolonged to 23.5 ± 1.0 days (P < 0.05). Standing oestrus lasted 47.2 ± 12.0 h (P = 0.09, n = 7). The interval from the onset of oestrus to ovulation was 59.4 ± 13.0 h (P = 0.08) and the interval from LH peak to ovulation 25.8 ± 1.3 h (P > 0.10). The prolonged oestrus was associated with increased (P < 0.05) growth of the ovulatory follicle and higher (P < 0.05) release of oestradiol-17β. Conception rates were 90% and 46% (P < 0.05), and the numbers of AI per heifer were 1.1 ± 0.1 and 3.4 ± 0.6 (P < 0.01) for control oestrous cycles and after treatment, respectively.The induction of suprabasal concentrations of progesterone caused asynchronies similar to those observed in cases of repeat breeding. The repeated AI did not maintain fertility at normal levels. It is suggested that the extended growth of the ovulatory follicle may cause impaired oocyte maturation or it may alter the maternal milieu owing to the prolonged release of oestradiol.     

Ovarian Activity at Naturally Attained Oestrus in the Sow. An Ultrasonographic and LH Study

In 6 multiparous crossbred sows (2nd to 4th parity, Swedish Landrace x Swedish Yorkshire), 15 proosestrous-oestrous periods during 2 oestrous cycles were studied after weaning. The animals were controlled for oestrus, and the follicular growth and ovulation in their ovaries were followed by transrectal ultrasonography. Blood was sampled through indwelling catheters for analyses of LH and progesterone (P4). The duration of oestrus (standing reflex) was 47 ± 12.4 h, and the interval from onset of standing reflex until the end of ovulation was 39 ± 12.4 h (range 20-64 h). The LH peak concentration was 3.7 ± 0.8 μg/1, and the interval from LH peak level until ovulation was 23 ± 8.4 h (range 8-32 h). The onset of standing reflex occurred in average 13 h before the LH peak level (range -4 - +36 h). The peripheral plasma concentration of P4 showed a normal cyclic pattern in all animals. Low levels (mean levels, 1.1-1.3 nmol/1) were seen during prooestrus and oestrus, high mean levels were found on days 10-16 (45-75 nmol/1) in the oestrous cycle. It was concluded that for an accurate determination of ovulation, each animal has to be examined repeatedly. Ultrasonography is a most valuable tool for this purpose.     

Reproductive characteristics of Chinese Hu sheep

The reproductive characteristics of Chinese Hu sheep are reviewed. Male and female lambs reached puberty at a mean age of 120 days and 180 days, respectively, with an average body weight of 18.54 ± 1.48 kg (n = 31) and 22.75 ± 1.98 kg (n = 24). Adult male and female sheep reproduced throughout the year. On average, ewes lambed 1.65 times per year (n = 1482). The mean ovulation rate of adult ewes was over 2.2 (n = 46). The average litter size of 150863 ewes raised under extensive conditions was 2.06. The early sexual maturity of male and female lambs was respectively related to high concentrations of testosterone and 17β-E₂ in blood plasma in the earlier postnatal period. The mechanism of high fecundity is not known.     

Synchronization of oestrus in gilts with altrenogest: effects on ovulation rate and foetal survival

Previous studies have shown that use of altrenogest resulted in a high rate of fertility and increased litter size compared with controls under conditions of practical pig production. The present study was designed to evaluate whether ovulation rate and/or foetal survival were increased by altrenogest using crossbred gilts derived from one herd (n = 227) and introduced in the same piggery over 12 months. Each gilt was allocated to a treated group (n = 103) receiving an individual daily dose of 20 mg of altrenogest for 18 days in its feed or a control group (n = 124) after puberty had been diagnosed, (197 ± 1 day; mean ± SEM). They were inseminated (double AI) at the second induced or natural oestrus. Pregnancy was diagnosed by ultrasonography at Days 22 and 42 post-insemination in the absence of return to oestrus. Pregnant gilts were slaughtered at 48 ± 3 days of pregnancy following the second examination. The number of living and dead foetuses were recorded before uterine contents (foetuses and placentae) were weighed and the number of corpora lutea (CL) per ovary counted.Precise synchronization of oestrus was observed after the end of the progestogen administration, with 93% of the gilts in oestrus by Days 5 to 7. For the controls, the interval from first to second oestrus ranged from 17 to 25 days in 93% of the control gilts. The pregnancy rate was 89.3% for treated gilts and 77.4% for controls (P < 0.05). The ovulation rate was increased by the treatment (15.4 ± 0.3 vs 14.6 ± 0.3; mean ± SEM, P < 0.02). Although the altrenogest group had more foetuses (11.1 vs 10.6), this difference was not significant (P > 0.14). The percent of foetal survival was similar in both groups (64.9%; P > 0.27). The foetal and placental weights differed only between dams and increased with stage of gestation. The increase in litter size through feeding altrenogest was associated with an increased ovulation rate.     

Nutrition level and season of birth do not modify puberty of Payoya goat kids

This study analysed the effect of level of nutrition and date of birth (age) on the onset of puberty in Payoya she-kids born in autumn (November) or in winter (February). Two experiments were conducted to examine pubertal events at the onset of puberty. For each date of birth (age), two experimental groups were used, differing on the level of nutrition. Groups were balanced for live weight (LW) and body condition score (BCS). For the first experiment (goat kids born in autumn), 27 Payoya she-kids were used: high-nutrition group (H1, n = 13) and control group (C1, n = 14). For the second experiment (goat kids born in winter), 25 Payoya she-kids were used: high-nutrition group (H2, n = 13) and control group (C2, n = 12). In both experiments, the level of feeding was adjusted weekly according to LW so that the animals would gain about 50 and 100 g per day for C and H groups, respectively. Oestrus was tested daily using young aproned bucks. Ovulation rate was assessed by laparoscopy 7 days after identification of oestrus. Plasma samples were obtained weekly for progesterone assay. LW and BCS were recorded weekly. No effect of nutrition level or birth date (Experiment 1 v. 2) on the date of the first ovarian activity or the first detected oestrus was observed. No effect of nutrition on LW or BCS at the first detected oestrus was observed. Birth date influenced significantly the LW of the animals at the onset of ovarian activity or first oestrus (P < 0.001). Irregular sexual activity was frequently observed before the first oestrus (74.7% and 48.0% of the first reproductive activity was irregular for Experiments 1 and 2, respectively). No effect of nutrition level or birth date on ovulation rate was observed. Ovulation rate at first oestrus was influenced by LW in November-born goat kids (1.06 ± 0.06 v. 1.67 ± 0.21 corpora lutea for LW < 30 and 30 kg, respectively, P < 0.01). These results demonstrate that the age at puberty was very dependent upon the season of birth in Payoya goat kids, and that there could be some benefit in breeding November-born goat kids at a higher LW to obtain a higher prolificacy at the first kidding as a consequence of a higher ovulation rate at puberty.     

Fasting-induced suppression of pulsatile luteinizing hormone secretion is related to body energy status in ovariectomized goats

The effect of energy status on the response of luteinizing hormone (LH) pulse frequency to acute short-term energy deficiency created by fasting in estradiol-treated ovariectomized Shiba goats was studied in two experiments. In experiment 1, eight goats whose mean body weight (BW) was 25.6 +/- 5.8 (mean +/- S.D.)kg were fed 500 g hay cubes daily for 1 week. Then they were fasted for 3 days. Blood samples were collected for 4 h at 6 min intervals on the last day of feeding, first, second and third day of fasting for LH analysis. The goats were divided into light (<24 kg, n = 4) and heavy (> or =24 kg, n = 4) groups for data analysis. There was no difference in LH pulse frequency between the last day of feeding and each day of fasting in the heavy group. LH pulse frequency was significantly (P < 0.05) suppressed on the second day (3.3 +/- 1.3 pulses/4 h) and on the third day (2.3 +/- 1.9 pulses/4 h) relative to the day prior to fasting (4.8 +/- 1.5 pulses/4 h) in the light group. In experiment 2, BW plus a body mass index (gBMI: (body weight (kg)/withers height (m)/body length (m)) x 10) were measured to define energy status. Nine goats (BW, 25.6 +/- 5.8 kg) were fed 500 g hay cubes daily for a week and then fasted for 3 days. Then they were divided into two groups offered either a maintenance (n = 4) or a restricted (n = 5) level of feeding for 4 weeks. The restricted level of feeding was 30% of maintenance requirement based on the BW recorded weekly. The feeding level was then adjusted to maintain BW for a further week followed by 3 day fasting for restricted animals. Blood samples were collected for 6 h at 10 min intervals on the day prior to fasting and on third day of fasting before and after the dietary manipulation. BW (26.6 +/- 2.2 to 26.8 +/- 3.8 kg) and gBMI (8.4 +/- 0.4 to 7.8 +/- 0.3) remained constant over the period prior to fasting for the maintenance animals but were significantly lower (P < 0.05) after 4 weeks for the restricted goats (BW, 26.3 +/- 2.1 to 21.5 +/- 2.4 kg; gBMI, 8.4 +/- 0.9 to 6.9 +/- 0.7). There was no significant difference in the LH pulse frequency between feeding and fasting day in both sampling periods in the maintenance group. In the restricted group, LH pulse frequency was not suppressed by fasting in the first sampling period (6.8 +/- 2.9 to 5.2 +/- 2.5 pulses/6 h), whereas it tended to be suppressed (4.8 +/- 3.1 to 1.6 +/- 2.3 pulses/6 h; P < 0.06) and was significantly (P < 0.05) correlated to body weight (r = 0.70) and gBMI (r = 0.81) after the dietary manipulation. These results suggest that the suppressive effect of short-term energy restriction (fasting) on pulsatile LH secretion is related to body energy status.     

Fertility of sows injected with exogenous oestradiol and/or gonadotrophins to control post-weaning oestrus

In the first of two experiments 28 multiparous sows were allocated to one of the following treatments 2 days after weaning at approximately 35 days post partum: (1) untreated; (2) i.m. injection 10 μg oestradiol benzoate (OB)/kg body weight (b.wt.); and (3) i.m. injection 20 μg OB/kg b.wt. Sows were bred at first post-weaning oestrus and ovulation rate assessed at slaughter. The mean interval from weaning to oestrus in each group was: (1) 5.6 ± 0.2; (2) 4.7 ± 0.2; and (3) 4.7 ± 0.2 days; the mean ovulation rates in groups 1 and 2 (18.7 ± 0.6 and 17.4 ± 1.8, respectively) were significantly higher (P < 0.01) than that of 12.0 ± 1.7 for treatment 3 sows. Two untreated and one each of the treated sows were not cycling at slaughter.In the second experiment 75 multiparous sows weaned at 28 ± 3 days post partum (day 0) were evenly allocated with respect to parity to one of four treatment groups: (1) untreated; (2) i.m. injection 10 μg OB/kg b.wt. on day 2; (3) PG600 (400 iu PMSG + 200 iu hCG) injection subcutaneous day 0; and (4) combined PG600/OB treatment as in (2) and (3) above. Sows were bred naturally at the first post-weaning oestrus and fertility assessed at farrowing. Control animals had a significantly longer (P < 0.05) weaning to oestrus interval (4.53 ± 0.25 days) compared to treatment 2 (4.03 ± 0.13) treatment 3 (3.97 ± 0.12) and treatment 4 (3.81 ± 0.07) sows. Sows treated with PG600 alone showed a significant increase (P < 0.05) in numbers born live compared to pre-treatment values. A smaller and non-significant increase in numbers born live in control sows (probably related to increasing parity) was not observed in either OB- or PG600/OB-treated animals.These results suggest that with further modification of the treatments, a system may be developed for introducing fixed-time artificial insemination (AI) or mating as a means of controlling the reproductive performance of the weaned sow.     

Superovulatory response of Chios sheep to PMSG during spring and autumn

To study the superovulatory response of Chios sheep to pregnant mares' serum gonadotrophin (PMSG), two experiments were carried out; one in spring and one in autumn. Four doses of PMSG (1500 IU, Group 1; 1000 IU, Group 2; 750 IU, Group 3; 500 IU, Group 4; controls, Group 5) were tested on 46 ewes. Oestrus was synchronised by means of MAP intravaginal sponges and PMSG was injected i.m. at the time of sponge withdrawal. When in oestrus, ewes were naturally mated. On Day 7 after sponge removal, mid-ventral laparotomy was performed and the uterine horns and/or oviducts were flushed with 20–40 ml Dulbecco's phosphate-buffered saline supplemented with 15% foetal bovine serum (FBS). The embryos were examined under a dissecting microscope and were evaluated according to morphological criteria.The interval from sponge removal to the onset of oestrus was significantly (P < 0.001) shorter in autumn than in spring in all groups. No significant differences regarding superovulatory response, collection and fertilisation rate or numbers of ova and embryos collected were found between spring and autumn. The clinical signs of oestrus started earlier (P < 0.001) in all PMSG treated animals than in the controls, both in spring and in autumn. The highest ovulation rate was recorded in Group 2 (5.9 ± 1.0), followed by Groups 1 (5.0±0.9), 3 (3.9±0.5), 4 (26±0.4) and 5 (1.3±0.1). The increase observed in total ovarian response (corpora lutea + large anovulated follicles) parallelled the increase of PMSG dose (10.7 ± 1.6, 7.7 ± 0.9, 4.5 ± 0.6, 3.4 ± 0.5 and 1.8 ± 0.2 for Groups 1, 2, 3, 4 and 5, respectively). The highest mean number of ova was collected from Group 3 (3.4±0.5), followed by Groups 2 (2.6 ± 0.4), 4 (2.2 ± 0.3), 1 (1.6 ± 0.5) and 5 (1.1 ± 0.1). The higher doses of PMSG (1500 and 1000 IU) significantly increased the mean number of anovulated follicles and significantly decreased recovery rate. Mean number of high viability embryos collected per ewe treated (0.9 ± 0.6, 1.5 ± 0.4, 2.2 ± 0.5, 1.5 ± 0.4, 0.9 ± 0.1 for Groups 1, 2, 3, 4 and 5, respectively) was not improved by PMSG dose.It is concluded that Chios sheep can be superovulated in autumn and in spring with similar results. Clinical signs of oestrus are initiated earlier in autumn than in spring. PMSG treatment shortens the interval from sponge removal to the onset of oestrus. Although PMSG does not seem to be the most suitable hormone for the induction of superovulation in Chios sheep, a dose of 750–1000 IU PMSG gives satisfactory results; higher doses are associated with side effects in a significant number of animals (many anovulated follicles, low recovery rate).     

Effect of nutritionally induced liveweight differences on ovulation rates and the population of ovarian follicles in ewes

Differential feeding prior to the onset of the breeding season resulted in mean liveweight differences of 12 kg in two groups of Romney ewes. This difference was maintained while ovulation rates and the population of externally visible ovarian follicles were measured. The ovulation rate at first oestrus was significantly higher in the high liveweight group but there was no difference between groups thereafter. High liveweight ewes had consistently higher mean follicle scores at all stages of the oestrous cycle. Mean follicle score was lower following the third oestrus than following first oestrus (P < 0.01).     

Time of ovulation in nulliparous and multiparous goats

Fifteen nulliparous and nine multiparous Serrana goats were used, through two successive oestrous cycles, in order to characterize their ovulation time with regard to the number of ovulations after induced and natural oestrus during the breeding season. The onset of oestrus was detected by the amount of vasectomized bucks after oestrus synchronization with prostaglandin, given 10 days apart, and in the following two expected natural oestrus. The preovulatory LH peak was determined from blood samples collected 0, 4, 8, 12, 16, 20 and 24 h after onset of oestrus. A transrectal ovarian ultrasound scanning was performed 20, 24, 28, 32, 36, 40, 44 and 60 h after onset of oestrus, for the detection of ovulations by means of the disappearance of large follicles (>4 to 5 mm). Single ovulations were observed in 76% of oestrous periods in nulliparous goats and in 18% of nulliparous goats. The onset of oestrus to LH peak interval was lower in nulliparous (12.1 ± 0.9 h, n = 38) than in multiparous (15.6 ± 1.0 h, n = 22, P < 0.05) goats with no oestrus interaction effects (P > 0.05). The LH peak to first ovulation interval was higher after natural (18.9 ± 0.7 h, n = 36) than after induced (15.8 ± 1.2 h, n = 24, P < 0.05) oestrus. The onset of oestrus to total ovulation interval was influenced by parity (P < 0.01) and oestrus type (P < 0.05) with a length of 30.1 ± 1.1 h (n = 15) and 33.4 ± 1.5 h (n = 9) for induced oestrus of nulliparous and multiparous goats, respectively, and 32.5 ± 1.0 h (n = 23) and 36.5 ± 1.1 h (n = 13) for natural oestrus of nulliparous and multiparous goats, respectively. The onset of oestrus to first ovulation interval was not influenced by parity, but an interval of 8.0 ± 1.6 h was observed between the first and second ovulations in polyovulatory oestrus. Consequently, nulliparous goats that are predominantly monovular ovulate earlier than multiparous goats that are predominantly polyovulatory. In conclusion, significant differences occurred in the number and time of ovulations between nulliparous and multiparous goats. More research is necessary for a deeper understanding of the mechanisms regulating monovularory and polyovulatory oestrous cycles regarding the parity of goats.     

Differential Metabolic Effects of Energy Restriction in Dogs Using Diets Varying in Fat and Fiber Content

The role of dietary fat and fiber in energy restriction for the management of obesity was examined. Twelve male castrated dogs were energy restricted for 7 weeks by feeding 60% of their calculated maintenance energy requirements (MER = 1500 kcal/m²/d) for ideal body weight. Six dogs were restricted on a high-fat (35.4 kcal% from fat), low-fiber (2.9% dry matter basis [DMB]) diet while the other six dogs were restricted on a low-fat (24.5 kcal% from fat), high-fiber (27% DMB) diet. Compared with the high-fat, low-fiber diet, energy restriction on the low-fat, high-fiber diet resulted in significantly greater decreases in body fat (1472 ± 166 vs. 853 ± 176 g; p < 0.05) and total serum cholesterol concentrations (108.7 ± 11.3 vs. 51.5 ± 13.9 mg/dL; p< 0.005). Reductions in body weight (2.86 ± 0.3 vs. 2.14 ± 0.3 kg; p< 0.09), and mean arterial blood pressure (17.4 ± 6.1 vs. 6.7 ± 2.9 mmHg; p < 0.12) were also greater on the low-fat diet; however, these diet effects did not reach statistical significance. These data suggest that the fat and fiber content of the diet during energy restriction are important factors in the management of obesity.     

Twenty-four-hour rhythm patterns of plasma melatonin in short-day and long-day breeders maintained under natural environmental conditions

ABSTRACT

Photoperiodic treatments have been of practical interest in controlling seasonal reproduction in sheep, goats and horses. Melatonin is the principal mediator of the environmental photoperiodic message. To investigate the intra- and inter-subject variability of melatonin 24 h rhythm, ten female Italian Saddle horses (8–10 yrs old, mean body weight 525 ± 30 kg), ten female Sarda breed sheep (2–3 yrs old, mean body weight 40.5 ± 2.8 kg) and ten female Sarda breed goats (3–4 yrs old, mean body weight 38.9 ± 4.1 kg), housed individually in a 4 × 4 m soundproof box equipped with 50 × 100 cm opening windows, were subjected to a natural photoperiod of the vernal equinox (sunrise 06:00 h; sunset 18:00 h). Blood samples were collected from each animal, every 3 h over a 48 h period starting at 00:00 h of day 1 and ending at 00:00 h of day 3. Plasma melatonin concentrations were determined by direct radioimmunoassay (MelatoninDirect RIA, Labor Diagnostika Nord GmbH, Nordhorn, Germany). The application of single cosinor method substantiated a circadian rhythm of melatonin with a nocturnal peak in all studied species. The application of two-way ANOVA on the rhythmic parameters indicated statistically significant differences between the three species in all of the cosinor analysis-derived parameters of MESOR, amplitude, acrophase and robustness of rhythm. Analyses of intra- and inter-subject variability indicate that organization of the melatonin 24 h rhythm is characterized by great accuracy of control within and between the individuals of a breed. In conclusion, features of the 24 h rhythm of melatonin among species; however, the 24 h rhythmicity of melatonin each species showed high stability within the various subjects and within the same subject. These findings must be taken into consideration when applying photoperiod and melatonin treatments for breeding purposes.     

Circadian modulation of starvation-induced hypothermia in sheep and goats

Prolonged food deprivation is known to cause a fall in the core body temperature of homeotherms. In various species of small birds and mammals (body mass up to 2–3 kg), it has been shown that starvation-induced hypothermia is modulated by the circadian system, in the sense that hypothermia is observed primarily during the inactive phase of the daily activity cycle (i.e., during the night for diurnal animals and during the day for nocturnal animals), whereas relatively normal temperatures are recorded during the active phase. To investigate whether this modulation occurs also in larger animals, we investigated the effects of 4d food deprivation on the body temperature rhythm of goats and sheep (body mass 30–40 kg). In goats, the body temperature rhythm was found to have a mean level of 39.0°C with a mean daily range of excursion of 0.42°C. The daily oscillation in body temperature persisted during the first day of fasting, but the rhythm was drastically damped, if not eliminated, over the next 3 d as body temperature descended from the baseline level of 39.0 to 38.2°C. In sheep, the rhythm was found to have a mean level of 39.3°C with a mean daily range of excursion of 0.34°C. The daily oscillation in body temperature persisted through the 4 d of food deprivation, even though the mean level of body temperature gradually fell. Temperature fell more during the third and fourth nights than during the third and fourth days. Thus, circadian modulation of starvation-induced hypothermia was observed in sheep but not in goats.     

Body weight as an effective tool for determination of onset of puberty in captive female Nile hippopotami (Hippopotamus amphibious)

Profiles of fecal progestogens and body weight from the early juvenile to the peri‐pubertal period are presented for eight captive female Nile hippopotami housed at Disney's Animal Kingdom in Florida. Average growth rate in juveniles was 0.85±0.03 kg/day (r²=0.913). Progestogen elevations were detectable as early as 16.8 months of age, and elevations indicative of ovulation and luteal activity were identified in seven of eight females by 30.3±1.6 months of age and body weight of 829.3±49.4 kg. Progestogen patterns before the onset of puberty were highly variable within and between females. Some females remained at baseline concentrations, whereas in others the progestogen pattern was characterized by infrequent, transient elevations of low amplitude and shortened duration. Four females were monitored through onset of puberty, conception, and first pregnancy. Onset of puberty was defined as the first luteal phase from the series of consecutive ovarian cycles culminating in conception and was observed at 34.9±2.2 months of age and 963.6±39.4 kg, however, the quality and number of cycles varied among females before conception. Females conceived between 2.7–3.9 years of age after attaining an approximate threshold body weight of 1,000 kg (1,070.5±39.5 kg). The age at first conception in captivity occurs at a younger age than has been reported for wild populations. Body weight may be an effective tool for approximating the state of reproductive maturity and facilitate collection management in zoos. Zoo Biol. 0:1–13, 2005. © 2005 Wiley‐Liss, Inc.     

Post-partum reproduction in swamp buffalo cows at two feeding levels

Post-partum progesterone secretion, oestrus, and conception were monitored in two groups of eight swamp buffalo cows which were fed at “low” or “high” levels from 12 weeks before until 36 weeks after calving. Calf birth weights and pre-weaning mortality were not affected significantly by nutritional treatment, but the average growth rates of calves from birth to weaning at 26 weeks of age were greater (P<0.01) at the high (0.39 kg/day) than at the low (0.26 kg/day) feeding level. In five cows from each group which reared calves to weaning, average post-partum intervals to first oestrus were 190 and 144 days (P<0.10), and average post-partum intervals to conception were 222 and 169 days (P<0.05), at the low and high feeding levels, respectively. Plasma progesterone profiles indicated that normal post-partum luteal function at both feeding levels was commonly preceded by transient corpora lutea with subnormal progesterone secretion. Mean body weights at conception did not differ significantly between the two groups, suggesting that earlier post-partum conception in cows at the high feeding level was associated with their lower body weight loss and/or their faster body weight recovery after calving.     

纳米硒对山羊生长、血清抗氧化酶、生长激素和胰岛素的影响

研究纳米硒对山羊生长性能、山羊抗氧化能力、生长激素和胰岛素的影响。选择体重相近、体格健壮的太行青山羊公羊90只,随机分为9组,分别喂以基础日粮和添加不同水平(0.03 mg/kg DM,0.05 mg/kg DM,0.1 mg/kg DM,0.3 mg/kg DM,0.5 mg/kg DM,1 mg/kg DM,3 mg/kg DM和5 mg/kg DM)纳米硒的饲料,实验期95 d。结果表明:日粮添加纳米硒显著提高山羊的生长性能(P<0.05)、血清超氧化物歧化酶和谷胱甘肽过氧化酶活性(P<0.05),当添加水平在0.3 mg/kg DM~1 mg/kg DM时,血清超氧化物歧化酶和谷胱甘肽过氧化酶活性保持高峰平台;日粮添加纳米硒显著降低血清谷胱甘肽硫转移酶活性和丙二醛含量(P<0.05),并在添加水平为0.3 mg/kg DM~1 mg/kg DM时保持低谷状态;日粮添加纳米硒显著提高全血硒、生长激素和胰岛素的浓度(P<0.05)。结论:日粮添加0.3 mg/kg DM~1 mg/kg DM,增强了山羊机体抗氧化功能,促进了生长激素和胰岛素的分泌,从而促进山羊的生长。     

Influence of perioestrous suprabasal progesterone levels on cycle length,oestrous behaviour and ovulation in heifers

In order to induce suprabasal plasma concentrations of progesterone after luteolysis and to determine their effect on oestrous behaviour and ovulation, heifers subcutaneously received silicone implants containing 2.5 (n = 4), 5 (n = 4), 6 (n = 3), 7.5 (n = 3) or 10 (n = 4) g of progesterone, or an empty implant (controls, n = 5) between days 8 and 25 of the cycle (ovulation designated Day 0). Growth of dominant follicles and time of ovulation were determined by ultrasound, and signs of oestrus were recorded and scored. Blood was collected at 2–4 h intervals from Days 15 to 27 and assayed for progesterone concentration. In all heifers, plasma concentrations of progesterone sharply decreased during Days 16–18. Control heifers had their lowest progesterone levels on Days 20.5 and 21, standing oestrus on Day 19.5 ± 0.4 (mean ± SEM), and ovulated on Day 20.7 ± 0.4. A similar pattern was observed in heifers treated with 2.5 and 5 g progesterone. Heifers treated with 6, 7.5 and 10 g of progesterone showed an extended (P < 0.05) interovulatory interval. Onset of prooestrus and time of maximum expression of signs of oestrus were not significantly different from those in controls. However, there was an absence of standing oestrus in most of the cases, signs of oestrus lasted longer (P < 0.05) and were weaker in intensity when doses increased. In these groups, the lowest progesterone concentrations were attained shortly after implant removal. Some heifers treated with 6 and 7.5 g of progesterone had standing oestrus and post oestrous bleeding as seen in the controls but ovulation occurred from Days 24.5 to 27. When plasma progesterone concentrations were over 1 nmol 1⁻¹, disturbed oestrus and delayed ovulation occurred. The extended period of prooestrus and oestrus and delayed ovulation were similar to that described in cases of repeat breeding. It is suggested that suprabasal plasma concentrations of progesterone, after luteolysis, may lead to asynchrony between onset of oestrus and ovulation and consequently be a cause of repeat breeding in cattle.     

Body condition is associated with a shorter breeding season and reduced ovulation rate in subtropical goats

To determine the effect of body condition on the characteristics of the breeding season in female goats from subtropical Mexico, does in either greater- or lesser-body condition (n=20/group) were monitored for the expression of estrous behavior, ovulation and ovulation rate between June and April. The commencement of estrus and ovulation occurred earlier (P<0.05) in does in greater than lesser body condition. The cessation of estrus and ovulation was later (P<0.05) in female goats with greater than those with lesser body condition. Does in greater body condition had more (P<0.001) normal estrous cycles than those in lesser body condition. As consequence, does from the greater body condition group had fewer short (P<0.001) or long (P<0.05) estrous cycles than those of in the lesser body condition group. The ovulation rate was greater (P<0.01) in the greater (1.9+/-0.1) than lesser body condition does (1.6+/-0.1). In conclusion, female goats in lesser body condition have a shorter breeding season, more abnormal estrous cycles, and fewer ovulations than does in greater body condition.     

Effects of food density and temperature on feeding and growth of young inland silversides (Menidia beryllina)

Food consumption and growth rates of 7–28-day-old Menidia beryllina were measured in response to natural ranges of temperature and prey availability. Feeding level, temperature and age all had significant effects on growth rate, although the effect of feeding level explained most of the variance. Feeding level also had a significant effect on gross growth efficiency, but temperature and age did not. Absolute growth rates (mg per day) increased dramatically with temperature, feeding level, and age. Variability in growth was greatest for fish feeding at the lowest feeding level. For a given fish weight, temperature had a positive effect on consumption rate, and maximum consumption ( C _max) of any treatment combination reached 75% body weight per day. Maximum growth rate was estimated at 24.6% body weight per day, and gross growth efficiency reached an estimated maximum of 0.375 at an ingestion rate of 25% body weight per day. Starved larvae lost on average 5.4% body weight per day and larvae required 6.4% body weight food consumption per day for maintenance. Multiple regressions of feeding level, temperature, and age/size on instantaneous growth rates indicated that increases in temperature increased maintenance requirements and required that fish consume a greater proportion of C _max to attain maximum growth. Growth rates decreased with increases in temperature for fish eating a specific weight of food.