Ovulation and ovulation rate in ewes under grazing conditions: factors affecting the response to short-term supplementation.

The relationships between ovulation rate and nutrition remain confused, probably because of uncontrolled variation in experimental conditions. To help resolve the problem, we analyzed data from 20 experiments conducted between 2002 and 2016, in Uruguay with grazing ewes. All experiments were carried out by a single laboratory under comparable conditions of experimental design and measured variables. The studies used a total of 3 720 ewes, of purebred Corriedale, Polwarth, or East Friesian x Polwarth genotypes. In all experiments, a control group grazed native pastures and extra nutrition was provided to the treatment groups using either improved pastures or supplements. Ovulation rate was measured by counting corpora lutea using laparoscopy or rectal ultrasound or by counting foetuses at ultrasound on day 45 of gestation. For statistical analysis, data were grouped according to nutritional treatment (control or supplemented) and, within these groups, type of supplement to provide energy or protein (protected or not from rumen degradation). Across all experiments, 92-99% of the ewes ovulated and the effects of diet, length of supplementation, and initial live weight and genotype are reported. Within diets, ovulation was most affected by overall energy intake during supplementation (P < 0.01). Ewes that grazed native pastures supplemented with protein supplements had higher ovulation rates (P < 0.05) than control ewes grazing only native pastures. The addition of tannins to the protein supplement, to protect it from degradation in the rumen, did not further increase the ovulation rate. In unsupplemented ewes that had access to legume pastures, ovulation rates did not increase when the legume pasture was rich in tannins although only ewes that grazed tanniniferous legumes had marginally higher ovulation rates than the control ewes (P < 0.05). When ewes grazing native pastures were supplemented with energy, their ovulation rate did not increase above those of nonsupplemented ewes. Live weight at the start of supplementation also affected ovulation rate. We conclude that ovulation was most affected by overall energy intake, whereas the factors that affected ovulation rate during short-tern nutritional supplementation were intake of protein from highly digested supplements or dietary protein protected from ruminal degradation.

Effect of early shearing during gestation on the productive and reproductive behavior of female sheep offspring in their first 18 months of age.

The research has shown the interesting contributions of shearing in mid-gestation on the performance of lambs from birth to weaning. Other studies have reported that shearing at early pregnancy influences the development of the placenta and lamb live weight at birth. However, there was a lack of information on the effect of early-prepartum shearing on the behavior of the offspring from weaning onward. This study evaluated the effect of shearing ewes at 50 days of gestation on the growth, reproductive behavior and response to a gastrointestinal parasite challenge in the female offspring from weaning to 18 months old. Fifty-seven Polwarth female lambs were used, 22 being singles and 35 twins born to ewes either shorn at 50 days of pregnancy (PS, n = 23) or shorn at 62 days postpartum (U, control, n = 34) resulting in four subgroups: single lambs born to PS ewes (n = 8), born to U ewes (n = 14), twin lambs born to PS ewes (n = 15) or born to U ewes (n = 20). All progeny were managed together under improved pasture with a minimum forage allowance of 6% live weight on dry basis. Body weight, body condition score and fecal eggs count were recorded every 14 days from weaning to 18 months of age. Concentrations of progesterone were measured weekly (from 4 to 10 months of age and from 14 to 18 months of age) to establish the onset of puberty. Ovulation rate at an induced and a natural heat (545 ± 1.0 and 562 ± 1.0 day old) was recorded. Prepartum shearing did not affect the age at puberty or the ovulation rate of female offspring, but those born as singles were more precocious ( P = 0.03) and heavier ( P = 0.02) at puberty than twin born lambs. Both the average value of parasite egg count ( P = 0.0 7) and the Famacha index ( P = 0.02) for the entire study period were lower in lambs born to prepartum shorn ewes than those born to postpartum shorn ewes. In conclusion, shearing at 50 days of gestation did not affect the growth or the reproductive behavior of female offspring. However, female lambs born from ewe shorn during gestation showed a better response to the parasitic challenge, and further research is required to confirm this.

Late-gestation protein restriction negatively impacts muscle growth and glucose regulation in steer progeny.

The objective of this study was to determine whether the amount of protein provided to cows during late gestation would affect postnatal growth and lead to changes in glucose and insulin concentrations. At 129 d of gestation, 10 mature multiparous Angus cows were stratified by body weight (BW) and body condition score (BCS) and allotted to either low protein level (LP, 6% crude protein [CP]) or high protein level (HP, 12% CP) groups. After calving, cows were managed together on improved pastures, which provided forage in excess of requirements until weaning. Male calves were maintained as a group after weaning on native range until 23 mo of age when individual steers were placed in single pens and fed a finishing diet for 84 d. The 12th rib fat thickness and longissimus muscle area were measured during finishing phase by ultrasound. Twenty days before the end of the finishing phase, steers were subjected to an intravenous glucose tolerance test. Steers were harvested and carcass characteristics collected. Cows' BW and BCS were similar at the initiation of treatment. During treatment HP dams gained 21 kg, whereas LP dams lost 7 kg (P = 0.04). Protein nutrition during late gestation did not influence calf birth weight, BW at weaning, adjusted 205 d BW, or average daily gain during lactation (P > 0.10). Longissimus muscle area measure by ultrasound was greater (P = 0.02) in HP steers at the beginning and end of finishing phase. Fat thickness of the 12th rib was not different (P > 0.10) between treatments. Glucose concentration after intravenous administration decreased (P = 0.002) in LP compared with HP steers. Peak of serum insulin concentration was greater (P = 0.04) and serum insulin concentration tended to decrease (P = 0.08) more rapidly in LP compared with HP steers after glucose infusion. At harvest, hot carcass weight was similar between treatments, but dressing percentage was increased (P = 0.05) in HP compared with LP steers. These data demonstrate that a lower protein nutrition level of dams during late gestation affect carcass characteristics and alter glucose regulation enhancing insulin secretion in steer progeny.

Growth, meat and feed efficiency traits of lambs born to ewes submitted to energy restriction during mid-gestation.

The objective of this study was to evaluate the effects of the energy restriction of gestation of adult ewes from day 45 to day 115 on lamb live performance parameters, carcass and meat traits. In experiment I, dietary energy was restricted at 70% of the metabolizable energy (ME) requirements, after which ewes were re-fed ad libitum until lambing. In experiment II, dietary energy was restricted at 60% of the ME requirements, and ewes were re-fed to ME requirements until lambing. All ewes grazed together from the end of the restriction periods to weaning. Lambs were weaned and lot fed until slaughter. Feed intake, weight gain and feed efficiency were recorded, and body fat thickness and ribeye area (REA) were measured in the longissimus thoracis muscle. After slaughter, carcass weight and yield, fat depth, carcass and leg length, and frenched rack and leg weights and yields were determined. Muscle fiber type composition, Warner-Bratzler shear force, pH and color were determined in the longissimus lumborum muscle. In experiment I, energy restriction followed by ad libitum feeding affected lamb birth weight (P0.05) were observed on later BW, REA, BF or carcass traits. Lambs born to non-restricted-fed ewes had higher (P<0.05) weight and yield of the frenched rack cut and their meat tended (P=0.11) to be tender compared with that of lambs from restricted ewes. The percentage of oxidative muscle fibers was lower for lambs born to non-restricted ewes (P<0.05); however, no effects of ewe treatment were observed on other muscle fiber types. For experiment II, energy restriction followed by ME requirements feeding, affected (P<0.01) pre-weaning live weight gain, weaning and final weights. Lambs from restricted ewes had higher (P<0.05) feed intake as % of leg weight and a trend to be less efficient (P=0.16) than lambs from unrestricted dams. Ribeye area and BF were not influenced by treatment. Treatment significantly affected slaughter weight, but had no effects on carcass yield and traits or on meat traits. The results obtained in both experiments indicate submitting ewes to energy restriction during gestation affects the performance of their progeny but the final outcome would depend on the ewe's re-feeding level during late gestation and the capacity of the offspring to compensate the in utero restriction after birth.

Minimizing cows' stress when calves were early weaned using the two-step method with nose flaps.

Early weaning may be used in beef cattle production to improve reproduction rates in range conditions. However, weaning causes a stress response in cows, which may be especially strong in early weaning management, as the bond between the cow and the calf is still strong. We hypothesized that weaning calves in two steps, with the aid of anti-sucking devices (nose flaps) would reduce the behavioural stress response in the cows separated from their calves 2 months after parturition. We compared the behaviour frequency and weight change in cows that were weaned abruptly, by separation of the calf on day 0 of the study, or in two steps, consisting of the use of anti-sucking nose flaps for 5 days before permanent separation; a third group was not weaned to serve as control. Thirty-six crossbred multiparous Aberdeen Angus×Hereford cows and their calves (n=12/treatment) were managed in three paddocks with similar pasture availability, with four dyads from each treatment per paddock. Cows' behaviour was observed by direct visual instantaneous sampling, at 10 min intervals from days -3 to 11. Weaning the calves in two steps clearly attenuated the behavioural stress response observed in abruptly weaned cows, which included reductions in grazing and lying, and increases in pacing, walking and vocalizing. Our results corroborate those previously shown for cows nursing older calves, and indicate that step weaning can reduce the behavioural stress response of cows at weaning, even when the calf is weaned shortly after birth, when the bond between the cow and calf is still very strong.

Colostrum production in ewes: a review of regulation mechanisms and of energy supply.

In sheep production systems based on extensive grazing, neonatal mortality often reaches 15% to 20% of lambs born, and the mortality rate can be doubled in the case of multiple births. An important contributing factor is the nutrition of the mother because it affects the amount of colostrum available at birth. Ewes carrying multiple lambs have higher energy requirements than ewes carrying a single lamb and this problem is compounded by limitations to voluntary feed intake as the gravid uterus compresses the rumen. This combination of factors means that the nutritional requirements of the ewe carrying multiple lambs can rarely be met by the supply of pasture alone. This problem can overcome by supplementation with energy during the last week of pregnancy, a treatment that increases colostrum production and also reduces colostrum viscosity, making it easier for the neonatal lamb to suck. In addition, litter size and nutrition both accelerate the decline in concentration of circulating progesterone that, in turn, triggers the onsets of both birth and lactogenesis, and thus ensures the synchrony of these two events. Furthermore, the presence of colostrum in the gut of the lamb increases its ability to recognize its mother, and thus improves mother-young bonding. Most cereal grains that are rich in energy in the form of starch, when used as supplements in late pregnancy will increase colostrum production by 90% to 185% above control (unsupplemented) values. Variation among types of cereal grain in the response they induce may be due to differences in the amount of starch digested post-ruminally. As a percentage of grain dry matter intake, the amount of starch entering the lower digestive tract is 14% for maize, 8.5% for barley and 2% for oats. Supplements of high quality protein from legumes and oleiferous seeds can also increase colostrum production but they are less effective than cereal grains. In conclusion, short-term supplementation before parturition, particularly with energy-rich concentrates, can improve colostrum production, help meet the energy and immunological requirements for new-born lambs, and improve lamb survival.

Effects of a short-term increase in the nutritional plane before the mating period on metabolic and endocrine parameters, hepatic gene expression and reproduction in primiparous beef cows on grazing conditions.

Sixty-four spring-calved primiparous crossbred cows paired by calving date and body condition score (BCS) at calving were used to study the effect of a short-term increase in the nutritional plane before the mating period on cow and calf performance, changes in metabolic and endocrine parameters and hepatic gene expression. At 48 ± 10 days post-partum (onset of nutritional treatment = day 0), cows were assigned to two treatments during 23 days: control (grazing of native pastures; NP; n = 31) and increased nutritional plane (NP improved with Lotus subbiflorous cv Rincon; IP; n = 33). Cow body weight (BW), BCS and total protein and albumin concentrations increased while urea and non-esterified fatty acids levels decreased from the beginning of the nutritional treatment in both groups, indicating the animal positive energy balance as forage growth and availability of pastures increased during spring. In addition, cow BW and BCS, as well as calf average daily gain and BW, were greater in IP than in NP cows groups. Insulin concentrations were less in IP than in NP (1.37 vs. 2.25 ± 0.26 µU/ml) because insulin increased owing to nutritional treatment only in NP cows. Hepatic insulin receptor mRNA at day 23 tended to be 1.5-fold greater, while insulin growth factor binding protein-3 mRNA expression was 1.7-fold greater in NP than in IP cows. Reproductive responses were not affected by nutritional treatment, but days to initiation of ovarian ciclicity (108 ± 10 days) were positively correlated with insulin concentrations. Grazing of improved NP for 23 days before the mating period did not improve cow reproductive performance but modified metabolic, endocrine and gene expression parameters, in agreement with greater nutrient and energy partitioning towards milk production, reflected in better calf performance.

Behavioral and physiological changes in early-weaned multiparous and primiparous beef cows.

Early weaning is used to advance postpartum ovulation in beef cows, but triggers a stress response, affecting cows' and calves' welfare. Our aim was to compare the response to early weaning in multiparous and primiparous cows. Seventy-one days after birth, calves from 14 primiparous and 11 multiparous cows were weaned. Since birth, cow's body weight (BW), body condition (BC), milk yield and calves' BW were recorded. Basophil/neutrophil relationship, total protein and albumin concentrations were measured before and after weaning. The distance between each cow and its calf before weaning, as well as main behaviors of the cows before and after weaning were recorded using 10 min scan sampling. BW and BC were greater in multiparous than in primiparous cows (P < 0.0001 for both). There was an interaction between parity (P = 0.004) and gender of the calf (P = 0.007): both BW and BC were greater in multiparous than primiparous cows, but multiparous cows with male calves had lower BW and BC than those with females (P < 0.001 for both variables). Milk yield was greater in multiparous than in primiparous cows (P = 0.02), and there was an interaction, with greatest milk yield in multiparous cows that calved males (P = 0.02). Total protein blood concentration increased with time (P < 0.0001), similarly in both groups. Albumin concentration profiles were similar despite parity, and decreased since 10 days after weaning (P < 0.0001). Basophil/neutrophil ratio was not affected by parity, and increased the day of weaning, remaining high until day 10 (P < 0.05). Frequency of standing decreased during the 2 days after weaning, with a greater decrease in multiparous than in primiparous cows (P < 0.0001). Pacing increased after weaning (P = 0.001), but increased significantly more in multiparous cows (P = 0.006), with a significant time after weaning by parity interaction (P = 0.01) reflected in greater frequencies in multiparous cows in the 2 days. Walking increased with time (P < 0.0001), and was more frequent in primiparous cows (P = 0.008). Ruminating, which was less frequent in multiparous cows (P = 0.014), decreased and remained low during the 3 days following weaning (P < 0.0001), but there was a significant time by parity interaction (P < 0.0001). The frequency of vocalizations increased dramatically after weaning (P < 0.0001), and was greater in multiparous cows (P = 0.006), and decreased more slowly during the 2nd and 3rd days after weaning (P = 0.005) in these animals. In conclusion, behavioral changes induced by weaning were greater in multiparous than primiparous cows, indicating a more intense response to cow-calf separation in the multiparous animals.

Response to biostimulation in peri-puberal beef heifers: influence of male-female proximity and heifer's initial body weight.

The objectives were to determine if exposure of 12 mo old peri-puberal beef heifers to androgenized steers for 35 d hastened puberty, and if the response was related to the physical proximity between males and females and to heifer's initial body weight. Hereford x Aberdeen Angus heifers (n = 131), 12 mo old, were assigned to two treatments: 1) Exposed group, exposed to androgenized steers from Day 0 to Day 35 (E, n = 66); or 2) Control group, isolated from the steers and other males (C, n = 65). Cyclic activity was determined through estrous behavior detection (twice daily) and weekly ultrasound imaging to detect a CL. For each Exposed heifer, an association index (with males) was determined thrice weekly, based on the distance to androgenized steers every 10 min for 4 h (until cyclic activity began). Data were analyzed according to heifer's initial body weight, which was categorized into three ranges (low, medium, and high, designated LW, MW, and HW, respectively). The cumulative proportion of cyclic heifers was greater for Exposed than Control heifers as of Day 21. By the end of the exposure period, more Exposed than Control heifers had attained puberty (16/66 vs. 2/65; P < 0.001). Within the HW classification, more Exposed than Control heifers became puberal (11/20 vs. 2/21; P = 0.002). However, there were no differences between MW and LW in the proportions of heifers that reached puberty. Association index in Exposed heifers was greater in HW than in MW and LW (0.10 +/- 0.09 vs. 0.06 +/- 0.03 and 0.06 +/- 0.04; P < 0.05), and in heifers that began cyclic activity compared to those that did not in the MW heifers (0.09 +/- 0.05 vs. 0.05 +/- 0.02; P = 0.01) and tended to be different in the HW treatment (0.12 +/- 0.10 vs. 0.06 +/- 0.02; P = 0.09). In conclusion, exposure of peri-puberal beef heifers to androgenized steers for 35 d advanced puberty in heavier heifers; an earlier response occurred in heifers with greater proximity to androgenized steers.

Effect of suckling restriction with nose plates and premature weaning on postpartum anestrous interval in primiparous cows under range conditions.

Suckling and nutrition are generally recognized as two major factors controlling the duration of the postpartum anovulatory period. In the present study, the effect of premature weaning and suckling restriction with nose plates (NPs) on cow and calf performance was evaluated. The study was conducted over 2 years; primiparous Hereford cows, weighing (mean+/-S.E.M.) 344+/-3.5kg and with 4.1+/-0.05 units of body condition score (BCS) (scale 1-8 [Vizcarra, J.A., Ibañez, W., Orcasberro, R., 1986. Repetibilidad y reproductibilidad de dos escalas para estimar la condición corporal de vacas Hereford. Investigaciones Agronómicas 7 (1), 45-47]) at calving, remained with their calves until 72.5+/-1.2 days postpartum (day 0). They were then assigned to one of three treatments: (i) calves with free access to their dams and ad libitum suckling (S, n=29); (ii) calves fitted with NPs for 14 days, but remained with their dams (NP, n=29), and (iii) calves that were weaned from their dams (W, n=28). All cows were anestrus at the time treatments commenced (day 0). All cows were blood sampled twice weekly from 1 week before the beginning of the experiment until the end of the mating period (day 74) for progesterone analysis. The mating period began on day 14. Cows in W treatment had ovulations earlier (P<0.05) than those in NP and S groups. Cows in the NP group had longer (P<0.05) intervals between the first progesterone increase and normal luteal phase than cows in the other two treatments groups (23.3+/-3.2 vs. 6.5+/-3.2 and 5.2+/-3.3 days for NP, S and W cows, respectively). Fifty per cent of the cows with NP had a short cycle (7 days) but there was a group of cows that had longer (P<0.05) intervals (66 days) between first progesterone increase and normal estrous activity. In the NP group, 8 of 29 cows had a short luteal phase and then a normal one; for 9 of these 29 cows progesterone concentrations remained low for 6 weeks from the beginning of the treatment; and for 12 of these 29 cows progesterone concentrations initially increased after treatment initiation, but these animals became anestrus thereafter. Short-term suckling restriction with NPs led to a variable response in primiparous cows of moderate body condition under range conditions.

A pre-partum lift in ewe nutrition from a high-energy lick or maize or by grazing Lotus uliginosus pasture, increases colostrum production and lamb survival.

This experiment tested the hypothesis that a lift in the nutrition of ewes, before lambing, to increase colostrum production would enhance lamb survival. In all, 261 mature Corriedale ewes, each with a single fetus from a synchronised mating, grazed native pasture to day 130 after mating; at which point they were weighed, condition scored and allocated to graze either native pasture or a pasture dominant with Lotus uliginosus. Five days later (14 days before the expected start of lambing) the ewes were allocated to one of four treatments and fed: (i) native pasture alone, (ii) native pasture plus a commercial high-energy lick, (iii) L. uliginosus pasture alone or (iv) L. uliginosus pasture plus whole maize. The weight, viscosity and concentration of components and immunoglobulin G in the colostrum that had accumulated at parturition, were measured for 10 ewes in each treatment. The lambs that survived to 20 days of age from the 221 ewes that were not milked, were recorded. The ewes supplemented with the lick or maize grain and those that grazed the L. uliginosus pasture alone accumulated two to three times more colostrum at birth than the ewes that grazed native pasture alone (396, 635 and 662 g v. 206 g; P < 0.01). The colostrum from the ewes that grazed only native pasture was more viscous (lower score) than that from the ewes supplemented with the lick or maize grain or the ewes that grazed the L. uliginosus pasture alone (scores of 4.1 v. 6.2, 6.5 and 6.4, P < 0.001) and, not surprisingly, the concentration of lactose in the colostrum of the ewes fed only native pasture was also much lower (1.1% v. 3.0%, 2.8% and 2.6%; P < 0.001)he survival of lambs from the ewes fed only native pasture was less than that of the lambs from ewes fed native pasture plus the commercial lick (81.8% v. 95.5%; P < 0.05) or the L. uliginosus pasture alone (92.4%, P < 0.05), and also tended to be lower than that for lambs born to ewes fed L. uliginosus pasture plus maize (91.8%, P = 0.08). The concentration of glucose in the blood of the lambs from the ewes that grazed only native pasture was lower than that of the other lambs (42.1 v. 60.2 ng/ml, P = 0.012). We conclude that the marked increase in colostrum production associated with the lift in ewe nutrition, just prior to lambing, enhanced lamb survival.

Lesions in the central nervous system associated with perinatal lamb mortality.

OBJECTIVE: To identify and describe the occurrence of neurological lesions that could have an effect on lamb mortality. PROCEDURE: The central nervous system was investigated macroscopically (n = 92) and microscopically (n = 72) in lambs dying in the perinatal period during 3 years in flocks of adult Corriedale ewes. The central nervous system was removed intact and samples of cerebral cortex, basal ganglia, thalamus, hippocampus, mesencephalon, cerebellar cortex, medulla oblongata, and cervical spinal cord were scored microscopically for the severity of neuronal dead, cytotoxic and perivascular oedema, and haemorrhage. RESULTS: Neurologic findings between birth and 6 days included haemorrhages in meninges, brain congestion and oedema, neuronal ischemic necrosis, intraparenchymal haemorrhages in medulla oblongata and cervical spinal cord, parasagittal cerebral necrosis, and periventricular leukomalacia. No significant lesions were found in anteparturient deaths or in those aged between 7 and 16 days. Oedema was more severe in the brain than in other regions of the central nervous system. Ischaemic neurons first appeared 24 hours post partum, increased linearly in number between 48 hours and 5 days post partum, and had a laminar distribution in the cerebral cortex, indicating a hypoxic-ischemic encephalopathy. Haemorrhages were most severe in the gray matter of medulla oblongata and cervical spinal cord, suggesting trauma due to instability of atlantoaxialis joint. CONCLUSION: Lesions in the central nervous system can explain most deaths at birth and within 6 days of birth. The lesions were hypoxic-ischemic and appeared to be related to birth injury.

Effect of supplementation of ewes with barley or maize during the last week of pregnancy on colostrum production.

The experiment tested the hypothesis that short-term feeding of barley just before lambing would be as effective as maize in stimulating early production of colostrum. Both grains are high in starch, and should provide a substrate for lactose which, in turn, promotes lactogenesis. Thirty-five Corriedale ewes bearing single foetuses and 25 bearing twin-foetuses from a synchronised mating were fed on pasture during most of gestation. Fourteen days before the expected time of lambing the single- and twin-bearing ewes were allocated to three treatments and fed (1) a basal diet of lucerne hay to meet their nutrient requirements, (2) the basal diet plus a supplement of whole barley; or (3) the basal diet plus a supplement of cracked maize. The twin-bearing control ewes accumulated more colostrum than the single-bearing control ewes at birth (292 v. 190 g). However, supplementation with barley or maize increased the colostrum at birth to 360 and 541 g in singles and 648 and 623 g in twins. We conclude that barley is a good alternative to maize to stimulate production of colostrum especially in twin-bearing ewes whose lambs are the most likely to benefit from the supplement.

Follicular growth and ovulation in postpartum beef cows following calf removal and GnRH treatment.

This study investigated the effects of calf removal (CR) and gonadotrophin releasing hormone (GnRH) administration on the duration of the postpartum anoestrous period in suckled beef cows. Experiment 1 involved 20 multiparous suckled cows that were assigned to each of two treatments on Day 61 postpartum: (i) unlimited access to their calves (C; n=10) and (ii) calf removal for a period of 96 h (CR96, n=10). Experiment 2 involved 24 multiparous cows that were assigned to each of two treatments on Day 63 postpartum: (i) CR96 (n=12); and (ii) CR96 plus 250 microg of GnRH administered on the day before calf return (CR96+GnRH, n=12). Experiment 3 was a 3x2 factorial experiment, involving 48 multiparous cows assigned to the experiment on Day 58 postpartum. The factors were C, CR96 and calf removal for 144 h (CR144), and 0 or 250 microg GnRH administered on the day prior calf return. In Experiment 1, the number of cows that ovulated within 12 days of calf removal was higher (P<0.05) in CR96 group (3/9) compared to the C group (0/10). In Experiment 2, all 12 cows in the CR96+GnRH group ovulated. In contrast only 4/12 cows in the CR96 group ovulated in response to calf removal. The diameter of the ovulatory follicle tended (P=0.06) to be smaller in CR96+GnRH cows (9.8 +/- 0.3 mm) than in CR96 cows (11.3 +/- 0.9 mm). The maximum diameter attained by the corpus luteum (CL) also tended (P=0.08) to be smaller for cows in the CR96+GnRH than for cows in the CR96 group (12.1 +/- 2.4 mm versus 16.7 +/- 7.5 mm, respectively). Plasma progesterone concentrations 12 days after calf removal tended (P=0.06) to be lower in CR96+GnRH cows than in CR96 cows (0.66 +/- 0.1 ng/ml versus 2.00 +/- 1.1 ng/ml, respectively). Few cows in the CR96+GnRH group regained normal cyclical activity and the interval from onset of calf removal to conception was longer (P<0.05) compared to cows in the CR group (52.2 +/- 5.7 days versus 20.0 +/- 6.6 days). In Experiment 3, 5/8 cows on the CR144 group and all 8 cows in the CR144+GnRH group ovulated. However, the interval from CR to conception was similar for all treatments. Temporary (96-144 h) calf removal, particularly in combination with GnRH treatment, can induce a high proportion of beef cows to ovulate, but the restoration of oestrous cycles may not be achieved.

Treatment of suckling beef cattle with a progestagen sponge and oestradiol benzoate or equine chorionic gonadotrophin.

The ovarian responses of anoestrus beef cows to a combined treatment with medroxy-progesterone acetate (MAP) sponges and oestradiol benzoate or equine chorionic gonadotrophin (eCG) were evaluated. Forty-five suckling Hereford cows were allocated to three equal groups. Group 1 received a MAP sponge for seven days plus an injection of 2 mg oestradiol benzoate when the sponge was inserted (day 0) and 1 mg when the sponge was withdrawn; group 2 received identical treatment until day 7, when a dose of 400 iu of eCG was administered, and group 3 were left untreated as control animals. From day 0 to day 11 the cows' ovaries were examined daily by transrectal ultrasonography, and their oestrous behaviour was observed from 24 hours to 96 hours after the sponge was removed. Data from cows that had a corpus luteum present before the sponge was withdrawn were not used in subsequent analyses; there were four in group 1, five in group 2 and four in group 3. In 19 of the 21 cows in groups 1 and 2 a new follicular wave was observed to emerge at a mean (sd) interval of 3.9 (0.3) days after the insertion of the sponge, whereas in group 3 it occurred in all 11 cows after 3.4 (0.6) days. Only the six cows that had a follicle of 9 mm or larger in diameter ovulated (P < or = 0.001). Nine of the 11 cows in group 1 came into oestrus, compared with two of the 10 in group 2 and none of the control cows (P < or = 0.001). Ovulation was observed in four, two and none of the cows in groups 1, 2 and 3, respectively.

Nutrition and colostrum production in sheep. 1. Metabolic and hormonal responses to a high-energy supplement in the final stages of pregnancy.

We tested the hypothesis that supplementation with cracked maize during the last week of pregnancy would provide ewes with a substrate for glucose and enhance the synthesis of lactose and, consequently, their production of colostrum. Thirty single- and 30 twin-bearing ewes were fed lucerne hay and half of each group was supplemented daily with 0.75 kg per head cracked maize during the last week of pregnancy. Colostrum production and the endocrine patterns in the animals were investigated. Supplementation with maize more than doubled the mass of colostrum available at birth in unsupplemented ewes: 339 v. 145 g in single-bearing ewes and 536 v. 197 g in twin-bearing ewes (P < 0.001). The total colostrum produced in the 10 h after birth was also significantly increased by supplementation: 730 v. 475 g in single-bearing ewes and 1259 v. 631 g in twin-bearing ewes (P < 0.01). The colostrum in the supplemented ewes was also more liquid with a viscosity score of 5.8 compared with 5.7 and 4.5 in unsupplemented single- and twin-bearing ewes (P < 0.01). Supplemented ewes had higher concentrations of lactose in their colostrum at parturition (2.6% v. 1.8% in single-bearing ewes and 2.5% v. 1.4% in twin-bearing ewes; P < 0.01). The plasma concentrations of progesterone and growth hormone in supplemented ewes were lower, whereas those of IGF-I and insulin were higher, all consistent with a higher capacity to produce colostrum. It is concluded that a high-energy supplement, like maize, fed to ewes in the last week of gestation increases their capacity to produce colostrum for their lambs, particularly for ewes bearing twins.

Nutrition and colostrum production in sheep. 2. Metabolic and hormonal responses to different energy sources in the final stages of pregnancy.

Lupins and maize, with similar concentrations of metabolisable energy, should produce similar responses in colostrum production at parturition when fed during the last week of pregnancy, but, in the present study, we tested the proposal that the physical form of whole lupins would restrict intake and, therefore, the response compared with cracked lupins or maize. Fifty-five twin-bearing ewes were divided into four groups: in the last 15 days of pregnancy, 14 were fed whole lupins, 13 were fed cracked lupins, 14 were fed cracked maize and 14 received no supplement. The cracked supplements were fed in increasing amounts for 6 days to avoid acidosis. The whole lupins were fed only from Day -8. All supplementary grains increased the intake of metabolisable energy by >35%, but only ewes eating maize accumulated significantly more colostrum at parturition: control, 207 g; cracked maize, 452 g; cracked lupins, 206 g; whole lupins, 231 g (P < 0.05). Plasma urea concentrations were extremely high (approximately 10 mmol L(-1)) for both groups eating lupins and approximately double those of control ewes or those receiving maize ( P < 0.05). We conclude that gut distention is not a cause of a poor response to lupins, but the ammonia associated with near-toxic concentrations of plasma urea may be affecting the production of colostrum.

Effect of diet and GnRH administration on post-partum ovarian cyclicity in autumn-lambing ewes.

Using autumn-lambing ewes, this study investigated (i) the effects of diet on gonadotrophin secretion and responsiveness of the hypothalamic-pituitary-ovarian axis to exogenous GnRH during the early post-partum period; and (ii) whether ovulation prior to completion of uterine involution results in an increased incidence of aberrant ovarian cycles. Thirty-two ewes rearing 1.9+/-0.12 lambs were equally allocated to two dietary treatments at lambing (22 October +/-0.2 day). Diets comprised ad libitum hay and 1.5 kg per ewe per day of one of two concentrates (11.5 MJ ME, 195 g CP per kg) containing 300 g kg(-1) cracked maize grain (M) or 300 g kg(-1) sugar beet pellets (S). Half of the ewes on each diet (G) received 25 i.v. injections of 250 ng GnRH in 2 ml 0.9% saline at 2 h intervals from days 12-14 post-partum while remaining ewes (N) were monitored for the resumption of spontaneous ovarian cyclicity. Blood samples were obtained from all ewes throughout the study (lambing to 18 December) for measurement of circulating hormone concentrations and the uteri and ovaries of all ewes were examined via laparoscopy on day 21 post-partum. There were no effects of dietary treatment on ewe daily live weight loss, lamb daily live weight gain or the immediate post-partum increase in circulating FSH concentrations. Diet did not affect insulin concentrations or LH pulse frequency on day 12 post-partum but LH pulse amplitude was lower in ewes fed concentrate M compared to concentrate S (1.4+/-0.10 versus 1.7+/-0.12 ng ml(-1), respectively, P<0.05) and this was associated with an increased interval to the resumption of spontaneous ovarian cycles (35+/-3.1 versus 26+/-2.1 day, respectively, P<0.05). Administration of exogenous GnRH increased (P<0.05) the proportion of ewes on both diets that ovulated within 20 days of parturition and advanced the onset of ovarian cyclicity in ewes fed concentrate M by 9.5 days (significance of interaction, P<0.05). Four ewes, all of which ovulated before day 22 post-partum, had extended luteal activity while in remaining ewes, duration of the first luteal phase was inversely related to the time of first ovulation (r(2)=0.16, P<0.05). Results demonstrate that (i) the onset of ovarian cyclicity is influenced by diet and can be advanced by administration of exogenous GnRH; and (ii) ovulation during the early post-partum period is associated with an increased incidence of extended luteal activity.