J. J. Robinson

Dietary excesses of urea influence the viability and metabolism of preimplantation sheep embryos and may affect fetal growth among survivors

In the first of two experiments investigating the effect of dietary urea on the survival and metabolism of ovine embryos, 30 Border Leicester x Scottish Blackface ewes received a maintenance diet (milled hay, molasses, minerals, vitamins) with no urea (control, C; n = 10) or with added urea at 15 g (low urea, LU; n = 10) or 30 g (high urea, HU; n = 10) kg-1 feed for a 12 week period. The degraded nitrogen (N) status relative to estimated rumen microbial N requirements was -2, +9 and +20 g per day, respectively. One week after allocation to diets, progesterone priming (12 days) commenced. Ewes received 800 IU of equine chorionic gonadotrophin at progesterone withdrawal, were inseminated 52 h later (Day 0) and embryos were collected from five ewes per group at Day 4 and from five ewes at Day 11. If available, one embryo was returned to each ewe; the rest were cultured in vitro. There was no effect of treatment on progesterone, luteinizing hormone (LH), or time of oestrus onset C, LU and HU plasma urea (P < 0.001) and ammonia levels (C vs. HU, P < 0.01; LU vs. HU, P < 0.05) differed. Day 4 HU embryos were retarded relative to C and LU embryos. After 3 days of culture, 70%, 66% and 0% of C, LU and HU embryos, respectively, were viable. Mid-term pregnancy rates following transfer were 63%, 43% and 33%. Only one HU lamb (male) was born following embryo transfer, its birthweight (10.1 kg) exceeded that of its C (n = 3; 7.0, 7.0, 7.5 kg) and LU (n = 2; 7.3, 8.2 kg) counterparts (P < 0.025). In the second experiment, C2 (2.5 g urea kg-1; n = 5) and HU2 (30 g kg-1; n = 7) diets which provided similar intakes of degraded N relative to microbial requirements as those for C and HU ewes in Experiment 1 were fed to Border Leicester x Scottish Blackface ewes superovulated with 16 mg of porcine follicle-stimulating hormone. Urea and ammonia levels in utero-oviductal samples were elevated in HU2 ewes (P < 0.05). At collection (Day 3), HU2 embryos used more glucose (P < 0.01) and, following culture, some exhibited up to a 2.8-fold increase in metabolism. In conclusion, excess rumen degradable N in ewe diets elevates urea and ammonia in plasma and in utero, with an associated increase in embryo mortality. Nevertheless, metabolism appears to be up-regulated in some embryos and, among those that survive, fetal growth appears to be enhanced.

Dietary-induced suppression of pre-ovulatory progesterone concentrations in superovulated ewes impairs the subsequent in vivo and in vitro development of their ova

In the first of three experiments, eight ovariectomised Greyface ewes primed with exogenous progesterone were used to provide quantitative data on the effects of two contrasting feeding levels (0.3 vs. 1.4 × maintenance) on plasma progesterone concentrations. Over the 9 day study period, mean (± SEM) daily progesterone concentrations were 4.3 ± 0.13 and 3.3 ± 0.17 μg l−1 for the low and high feeding regimens, respectively (P = 0.06), indicating that high feed intake suppressed circulating progesterone levels. The second experiment examined the effect in superovulated Finn-Dorset ewes of a diet supplying either 0.6 (Group L, n = 8) or 2.3 (Group H, n = 8) times their daily energy needs for maintenance, from 1 day before introduction of exogenous progesterone to the time of insemination, on plasma progesterone concentrations and the viability of ova recovered 4 days after insemination. Mean (± SEM) plasma progesterone concentrations were 4.5 ± 0.17 μg l−1 and 2.8 ± 0.16 μg l−1 for L and H ewes, respectively, during the 12 day priming period (P 0.10) at ovum collection. Intervals (mean ± SEM) to oestrous onset (14.5 ± 0.38 h) and the luteinising hormone (LH) surge (27.1 ± 0.98 h) were unaffected by feed intake. Mean (± SEM) ovulation rates (8.1 ± 1.57 vs. 7.8 ± 1.10) and numbers of ova recovered (5.0 ± 1.39 vs. 4.8 ± 1.11) were also similar for each group. However, the proportions of ova considered viable (over 32 cells) at recovery were 0.53 and 0.22 for L and H groups, respectively (P < 0.005). Following 72 h culture (Tissue Culture Medium-199 (M199) + 10% foetal calf serum (FCS)), 0.55 and 0.27, respectively, had developed to blastocysts (P < 0.025). Of ova assessed as viable at recovery, similar proportions (0.86 vs. 0.75) from L and H treatments developed to blastocysts, with corresponding nuclei counts (mean ± SEM) of 55 ± 5.2 and 55 ± 13.2. The third experiment used 12 superovulated Greyface ewes, each offered a different feed level within the range 0.6–2.5 × maintenance, to determine the nature of the relationship between feeding level, pre-ovulatory progesterone concentrations and ovum development at Day 2 following insemination and subsequently during 7 day co-culture (M199 + FCS). Increases in feeding level were accompanied by linear decreases in plasma progesterone (r2 = 0.79, P < 0.001), the interval to oestrous onset (r2 = 0.52, P < 0.01) and timing of the LH surge (r2 = 0.32, P < 0.06). Although undetectable at ovum collection, and somewhat equivocal after 4 day culture, high feeding levels prior to ovulation reduced the proportion of ova (0.16 vs. 0.58) developing to or beyond the expanding blastocyst stage after 7 day culture. Quantitative indices of cell division and protein synthesis confirmed this. In conclusion, excessive feeding during follicular recruitment and oocyte maturation in superovulated ewes imparts a legacy of embryonic loss and developmental retardation.

Effects of body fatness at lambing and diet in lactation on body tissue loss, feed intake and milk yield of ewes in early lactation.

Thirty-six mature Finnish Landrace × Dorset Horn ewes, each suckling two lambs, were used in a comparative slaughter experiment to measure changes in body tissues during early lactation. Two levels of body fatness at lambing were established by giving ewes a complete diet containing 10 MJ metabolizable energy (ME) and 139 g crude protein (CP)/kg d.m. either close to requirements or ad libitum during the second half of pregnancy. In lactation half the ewes in each group were given a complete diet containing either 90 (diet A) or 60 (diet B) % milled hay ad libitum . These diets contained 7·9 and 9·2 MJ ME and 121 and 132 g CP/kg d.m. respectively. Ewes fed at the two levels in pregnancy contained 8·4 and 19·6 kg chemically determined fat 5 days after lambing but had similar amounts of body protein, ash and water. Over 6 weeks of lactation ewes given diet A lost 60 and 69% of these weights of fat respectively, while ewes given diet B gained 5% and lost 30% respectively. Up to 26 g of body protein was lost daily from ewes given diet A but none from ewes on diet B. During early lactation the weight of the empty digestive tract increased while the weights of most other body components, particularly the carcass, decreased. The ratio of body energy change to live-weight change varied from 24 to 90 MJ/kg. Thus live-weight change did not accurately reflect relative or absolute changes in body energy. Voluntary food intake was greater for ewes given the high-energy diet (B) than for those given diet A and was depressed in the fatter ewes. Differences in intake could be explained by the effects of body fatness and diet on the weight of gut contents. Milk yield was not significantly affected by body fat reserves but was higher on diet B than A. Fat content of milk was higher and protein content lower for ewes with the higher fat reserves at lambing. As the contribution of fat loss to energy available for milk synthesis increased there appeared to be a reduction in the energetic efficiency of milk synthesis. A number of possible reasons for this are discussed.

Studies on reproduction in prolific ewes. 4. Sequential changes in the maternal body during pregnancy

Seventy-eight Finnish Landrace × Dorset Horn ewes in lamb to Suffolk rams were slaughtered serially between 50 and 145 days of gestation. The mean litter size was 2·7. The daily feeding regime aimed to provide each ewe with 15 MJ of metabolizable energy (ME) in the first month of gestation and 9·4 MJ in the second and third. Thereafter the ewes were provided with a basal intake of either 9·6 MJ (low plane, LP) or 13·4 MJ (high plane, HP) plus 1·3 MJ for each foetus. For ewes with 2, 3 and 4 foetuses the mean percentage changes in maternal body weight over pregnancy were respectively — 5, — 10 and — 14 (LP) or + 3, — 2 and — 6 (HP). Changes in weights of blood, liver and the empty gastro-intestinal tract through gestation varied with the plane of nutrition but not with number of foetuses. In contrast, udder weight at parturition was dependent on number of foetuses but not on plane of nutrition. Increased hydration of the maternal tissues in late pregnancy tended to mask concurrent losses of body fat. For example, over the last 2 months, HP ewes carrying quadruplets lost on average 1·0 kg in body weight but 5·5 kg of (chemically determined) fat. The latter was lost at a rate which increased up to an average of 170 g/day over the last 2 weeks of pregnancy. Net changes in body protein were estimated to be relatively small, but there was some redistribution, including loss from muscle and gain by the udder. There was no evidence of any demineralization of the maternal skeleton. The practical significance of the changes in body composition is discussed, in particular that of the increasing rates of loss of body fat with increasing litter size. It is suggested that the dangers implicit in these rates of fat loss must be taken into consideration when deciding on dietary regimes and the timing of breeding cycles for highly prolific ewes, or indeed when embarking on a programme of increased prolificacy.

Effects of protein concentration in the diet on milk yield, change in body composition and the efficiency of utilization of body tissue for milk production in ewes

Twenty-five mature Finnish Landrace × Dorset Horn ewes, each suckling two lambs, were used to measure the effects of dietary concentration of crude protein on food intake, milk yield and changes in body composition during the first 6 weeks of lactation. Diets were complete mixes of milled hay and concentrates, and the amounts of barley and fish meal were altered to give crude protein concentrations of 116 and 143g/kg dry matter. Ten ewes were slaughtered at 5 to 7 days of lactation and the remaining ewes were slaughtered at 40 to 43 days of lactation. The higher concentration of crude protein in the diet did not alter food intake or digestion. Milk yield was not altered in the first 3 weeks of lactation but was increased in weeks 4 and 5 (P It was concluded that the higher level of protein intake during early lactation increased yields of milk and milk protein. The data suggest that the energy lost from the body was used more efficiently by ewes given the diet of high, rather than low, protein content.

The effect in ewes of source and level of dietary protein on milk yield, and the relationship between the intestinal supply of non-ammonia nitrogen and the production of milk protein

Individually penned Finnish Landrace × Dorset Horn ewes in early lactation, and each suckling two lambs, were used to test the effects on milk yield, milk composition and the concentrations of some plasma constituents of supplementing a basal diet with either urea, groundnut, soya bean, linseed, fish, meat and bone, or blood meal. The basal diet contained 94 g crude protein and 10 MJ of metabolizable energy per kg dry matter and supplied daily 0·3 MJ of metabolizable energy per kg body weight. Except for urea, which was tested at an inclusion rate that increased the protein (nitrogen × 6·25) content of the basal diet by 43 g/kg, the remaining sources were tested at three levels, corresponding to increases in protein content of 34,60 and 86 g/kg. Daily milk yields were 1·92 and 2·08 kg for ewes given the basal diet and the basal diet supplemented with urea. For the high inclusion rates of each protein source the following daily yields were obtained (kg): groundnut, 2·26; soya bean, 2·45; meat and bone, 2·49; linseed, 2·68; fish, 2·84; and blood meal, 2·91. The daily yields of true protein in milk were (g): basal diet, 76; basal diet plus urea, 80; groundnut, 104; soya bean, 107; meat and bone, 105; linseed, 112; fish, 136; and blood meal, 125. Plasma concentrations of free fatty acids did not appear to support the hypothesis that the milk yield response to protein is accomplished solely by increases in tissue energy loss. The increment in the amount of non-ammonia nitrogen reaching the abomasum as a result of the low levels of inclusion of the protein sources in the basal diet was used for the production of true protein-nitrogen in milk with an efficiency of 0·58.

The modifying effects of melatonin, ram exposure and plane of nutrition on the onset of ovarian activity, ovulation rate and the endocrine status of ewes

Abstract In four experiments, ewes were kept in natural daylength conditions at 57 °N and given daily at 15:00 h an oral dose of 3 mg of melatonin. Irrespective of feeding level, this method of administering melatonin sustained plasma concentrations of the hormone at night-time values from 1 h after dosing to the onset of natural darkness (7 h or less), but by the following morning concentrations were the same as those for control ewes. For Experiment 1, which started on 6 July and involved 24 Border Leicester × Scottish Blackface ewes, the mean intervals and (ranges) in days to the onset of ovarian activity (plasma progesterone above 1 ng ml −1 ) were SO (40–61) and 70 (35–96) for melatonin-treated and control ewes kept in isolation from the male. Corresponding values for those exposed once daily to a vasectomized ram were 29 (5–44) and 34 (21–61). In Experiment 2, the intervals from the start of treatment on 6 June were 67(57–75) days for ten Scottish Blackface ewes receiving melatonin compared with 107 (75–141) for nine of ten controls that showed ovarian activity before the experiment ended on 29 October. For a further ten ewes exposed continuously to an cestrous ewe and vasectomized ram, the interval was 72 (36–124) days. Experiment 3 started on 10 June and involved 32 Scottish Blackface ewes which were exposed once daily to a vasectomized ram and received two levels of feeding (5.8 or 11.6 MJ of metabolizable energy daily), either with or without melatonin in a 2 × 2 factorial design. Here, the intervals to behavioural oestrus were 79 (70–91) days and 92 (71–111) days for treated and control ewes, respectively, given the low feeding level and 74 (57–86) days and 83 (70–102) days for those given the high feeding level. Melatonin increased the ovulation rate and litter size, with the increases being greater for the low-than high-plane ewes. In Experiment 4, the mean interval from the start of meiatonin treatment on 7 July to the onset of ovarian activity for low-plane Scottish Blackface ewes was 61 ± 12.5 days versus 78 ± 11.4 days for controls ( n = 10 per group). The ovulation rate at first behavioural oestrus was not affected by melatonin, but at the subsequent three oestrous cycles was always higher for those receiving melatonin. Melatonin decreased circulating prolactin concentrations and obliterated their circadian rhythm (Experiment 1). Luteinizing hormone concentrations in plasma samples taken at frequent intervals for up to 24 h at 1, 3, 6 and 9 weeks after the start of melatonin treatment (Experiments 1 and 3), favoured the hypothesis that it initiates ovarian activity in ewes via a sudden increase in the activity of the hypothalamic gonadotrophin-releasing hormone pulse generator just prior to oestrus, rather than by a gradual and progressive increase throughout the treatment period.

The prediction of body composition in live ewes in early lactation from live weight and estimates of gut contents and total body water

The efficacy of estimates of gut contents and total body water in increasing the precision with which the chemical composition of the body could be estimated in early lactation was evaluated in 36 Finnish Landrace × Dorset Horn ewes. The ewes were fed at two levels in pregnancy, and, in lactation, given diets of two metabolizable energy concentrations. The allometric relationships relating weight of chemical fat and protein to emptybody weight were not affected by treatment or stage of lactation. Inclusion of an index of gut contents, based on dry-matter intake, indigestibility and retention time of food residues, together with live weight in a regression equation predicting weight of body fat, only slightly increased the precision of estimate compared with equations using live weight alone. There was a close negative relationship between the proportions of water and fat in live weight. Inclusion of weight of body water with live weight in a regression equation predicting weight of body fat markedly increased the precision of estimate and the residual error (0·81 kg) was similar at different stages of lactation. However, when deuterium oxide space was used instead of body water there was only a small increase in precision of estimate and the residual error varied from 5·3 kg in early lactation to 2·1 kg in mid-lactation. The relationship between deuterium oxide space and body water was shown to be variable and altered by stage of lactation, and these differences were associated with differences in rate of water turnover in the animals body. It is concluded that estimates of body water are unsuitable for estimating weight of body fat in early lactation.

Daily oral administration of melatonin from March onwards advances by 4 months the breeding season of ewes maintained under the ambient photoperiod at 57 °N

Abstract In three experiments, ewes kept under the ambient photoperiod at 57 °N were given daily at 15:00 h from March onwards an oral dose of 3 mg of melatonin in a 4:1 mixture of water and ethanol or, in the case of controls, the vehicle alone. All ewes were challenged daily with a vasectomized ram for the detection of behavioural oestrus. In Experiment 1, the mean interval (± standard error of the mean (s.e.m.)) from the start of melatonin treatment on 5 March to first behavioural oestrus for Border Leicester × Scottish Blackface ewes that had remained barren over the winter period was 87 ± 5.8 days ( n = 8) compared with 222 ± 10.3 ( n = 7) for controls. Corresponding intervals from the start of melatonin treatment on 24 March for the same breed of ewe in Experiment 2 were 80 ± 3.7 ( n = 6) and 211 ± 9.4 ( n = 6) days. In Experiment 3, 22 Scottish Blackface ewes that lambed between 11 January and 22 February were paired by lambing date for weaning at either 6 or 14 weeks. All ewes received melatonin from 22 March until 5 August. Apart from one ewe from the 14 week group that failed to show oestrus, all other ewes responded to melatonin and exhibited first behavioural oestrus at mean intervals from initial dosing of 77 ± 4.6 days and 75 ± 3.2 days for the 6 week and 14 week groups, respectively. Melatonin suppressed prolactin in both dry (Experiments 1 and 2) and lactating ewes (Experiments 1, 2 and 3), but in the only experiment in which it was tested (Experiment 1), its continuous administration throughout pregnancy failed to prevent the late-pregnancy rise in prolactin. It had no effect on gestation length or the subsequent growth rate of lambs; its effect on lamb birth weight was equivocal, causing a significant decrease in twin lambs in Experiment 2 and no effect in Experiment 1. Detailed sequential measures of the nature of the episodic release of luteinizing hormone (LH) (Experiment 2) provided no evidence that melatonin induced a progressive increase in the activity of the gonadotrophin releasing hormone (GnRH) pulse generator. The ovarian response to the daily oral administration of melatonin from March onwards contrasts with literature reports on the failure of continuous-release implants of melatonin to stimulate behavioural oestrus when inserted as early as April or May.

The effect of physiological state on digestion in the ewe and its influence on the quantity of protein reaching the abomasum

Three experiments were carried out on Finnish Landrace × Dorset Horn ewes in various physiological states and given daily 2 kg of a diet containing equal parts of hay and concentrate. In experiment 1 six ewes, each fitted with cannulae in the rumen and abomasum, gave mean estimates for the proportion of their digestible organic matter intake that was apparently digested in the rumen of 0.50 in late pregnancy, 0.64 in early lactation and 0.65 post-weaning (P < 0.01). The quantities (g/d) of non-ammonia nitrogen reaching the abomasum were 46.9 for pregnancy, 36.4 for lactation and 40.4 post weaning (P < 0.001). In experiment 2 the time required to recover an oral dose of chromic oxide in the faeces was significantly (P < 0.001) lower for ewes in late pregnancy than for barren ewes and the effect was not influenced significantly by the physical form of the roughage (milled versus chopped). In experiment 3 the fractional outflow rate per hour of a chromium-mordanted fish meal supplement from the rumens of eight ewes in the 18th week of pregnancy was 0.053 compared with 0.044 for the same ewes in early lactation (P < 0.025). It is suggested that the stimulatory effects of pregnancy on the rate of outflow of material from the rumen and on the quantity of protein reaching the abomasum may play a role in the nitrogen economy of the pregnant ewe.