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The gain in genetic merit for milk production in the US (Foote, 1996) has been accompanied by a decline in conception to first service of approximately 0.45% per year (between 1975-1997, Butler and Smith, 1989; Beam and Butler, 1998). A similar trend is anticipated in the UK. Lamming and Darwash (1998) reported that defective ovarian function prior to insemination contributes to lower reproductive efficiency. In particular, persistent luteal activity was associated with reduced fertility and a higher incidence of late embryo mortality (embryonic death after day 16 post-insemination). The objectives of this study are firstly, to determine the current incidence of atypical ovarian hormone patterns and secondly, to make specific comparisons between the present results and those of our previous study.
Ovine embryos produced in synthetic oviduct fluid (SOF) medium or in coculture with granulosa cell monolayers supplemented with low (A; 120 μmol/l) and high (B; 190 μmol/l) ammonia-producing steer sera caused different degrees of fetal oversize (Carolan et al., 1998). The objective of the present study was to determine whether the effects on fetal growth induced by these sera were associated with alterations in early embryo development.
A total of 911 bovine oocytes, used in 8 replicates to test the effect of three culture treatments on embryo development, were matured and fertilized in vitro (IVF= Day 0). Presumptive zygotes were allocated on Day 1 to culture in SOF supplemented with 10% v/v steer serum (SOF+A, n=308; SOF+B, n=302) or with amino acids plus 0.4% w/v crystalline BSA (SOFaaBSA, n=301). All cultures were in 20 μl droplets under oil (38.5°C; 5% CO2, 5% O2; 4 zygotes per drop) and droplets were renewed every 48 h. Cleavage rate was recorded on Day 3. On Days 7 and 8, blastocyst yields, grade 1 and 2 blastocysts, their cell numbers (by staining with Hoechst 33342) and their stage and diameter were determined.
In farm animals early embryonic loss is recognised as a major cause of reproductive wastage. In sheep and pigs there is evidence that high energy intakes prior to ovulation and in early pregnancy depress systemic progesterone with a detrimental effect on embryo survival. The objective of this study was to investigate the effect of short term nutritional changes pre- and post-insemination on embryo survival and systemic progesterone in cattle. Preliminary results have been presented previously (Dunne etal., 1997).
Oestrus was synchronised in 247 beef cross heifers aged 18-24 months using two injections of prostaglandin (PG) administered 10 days apart. At the oestrus following the first PG injection heifers were allocated to either a Low (L, 0.6 M) or High (H, 2.3M) pasture allowance for the 10 day period prior to artificial insemination (AI). AI was carried out at the oestrus following the second PG injection using semen from a single Limousin bull. On the day following AI, heifers were randomly reallocated to either a L or H pasture allowance until embryo recovery at day 14 to 16 or pregnancy diagnosis at Day 30.
The prolonged interval from calving to first ovulation in beef cows is primarily due to the suckling-mediated inhibition of pulsatile LH release. Undernutrition both before and after calving also suppresses LH release, reduces ovarian follicular growth and delays ovulation. The interactive effects of these factors on the interval from calving to first ovulation in beef cows were quantified by studying the incidence of ovulation, following acute calf isolation and once-a-day suckling (restricted access), after emergence of the fourth follicular wave post partum in cows in differing body condition at calving and offered low or high planes of nutrition after calving.
The experiment was a 2 x 2 x 2 factorial design, in which the factors were body condition score at calving (Low v. Moderate), feeding level after calving (0.6 v. 1.0 MJ ME/d/kg M0.75), and restricted (once-a-day) v. ad libitum access and suckling. The experiment, duplicated at each of the four participating sites, involved 16 Simmental, 16 Sarda, 16 Brown Swiss and 16 Hereford x Friesian multi-parous cows. Follicle growth was monitored daily from day 21 post partum until the earlier of second ovulation or Day 90 post partum using transrectal ovarian ultrasonography.
The interval from calving to first ovulation is a major factor affecting reproductive and productive efficiency in beef cows. While this interval is affected by pre- and post-partum nutrition, the maternal-offspring bond is generally considered to be the major cause of delayed ovulation in beef cows. The endocrine and physiological mechanisms by which these factors either singularly or interactively control the duration of the post-partum anovulatory period are not well established, although they most likely involve the regulation of pulsatile LH release. The present study sought to examine the interactive effects of pre- and post-partum nutrition on LH secretion and follicle wave dynamics following acute calf isolation and once-a-day suckling (restricted access), after emergence of the fourth follicular wave post partum.
Recent MLC survey data (Pig Year Book, 1995) reports that approximately 0.5 of annual first parity gilt cullings are due to reproductive failure. This high culling rate may be attributed to recent genetic selection for increased lean tissue accretion rates, and as a result a greater mature body weight. However, the gilt attains puberty and is thus mated at a lower age and as a consequence has not reached the target threshold of 35kg body protein mass at farrowing, suggested by Everts (1994),to be necessary for optimal reproductive performance. This, confounded with excessive tissue catabolism over lactation results in the attenuation of the gilt's potential protein accretion curve and hence reproductive failure (Foxcroft et al. 1995). The aim of this experiment was to study the effect of two protein accretion rates (maximum and 0.8 of maximum) on reproductive function in the gilt from 50kg liveweight to 3rd oestrus.
Reproductive failure, especially in young sows, is the major contributor to the steady rise in sow culling and mortality rates in recent years. There is now considerable interest in the nutrition of the gilt and its effect on production characteristics and subsequent reproductive performance. Both fat, and more recently lean tissue, have been postulated to play singularly important roles. The objective of the current study was to use production performance criteria of both primiparous and multiparous animals to estimate the proportions of fat and lean tissue mobilised during lactation.
Ninety two animals, forty five gilts and forty seven third parity sows, based at the University commercial pig unit, were used in this study. All animals were weighed and monitored for P2 backfat depth on entry to the farrowing house, during lactation and, finally, at weaning. The data for each individual animal was then used to calculate, by linear regression, the daily rate of loss of both body weight and P2 backfat depth during lactation. These responses were then utilized to calculate the weight and P2 backfat level of each animal on days 1 and 28 of lactation.
Starch and fat are the two major energy sources available for sow lactation diets. Fat is more energy dense and can be used to maximise energy intakes, particularly in sows with low appetite. However, the quantity of milk produced in sows has been associated with milk lactose production and the main precursor for lactose is glucose, for which dietary starch is the major source. It is therefore important to know the consequences of using a glucose deficient energy source, such as fat, compared to starch in lactation diets. The following experiment was designed to assess energy sources in lactation diets at an isocaloric level in determining sow and piglet performance, in association with the effects of dietary glucose availability on the metabolic state of the sow around peak lactation.
Reproductive performance of modern lean genotypes of pig has been shown to be particularly sensitive to dietary protein (Sinclair et al. 1996, Cia et al. 1998). This experiment examined the effect of modifying body protein : lipid ratio at different absolute protein mass on ovarian function in lactating gilts. A partial weaning technique was used to increase the potential sensitivity of the reproductive axis to differing lactational dietary protein levels.
A 3x2 factorial experiment involving 60 first parity sows compared 3 different pregnancy feeding strategies and 2 lactation diets. During pregnancy, sows were fed from day 42 either a set quantity (mean of 2.27 kg/day) of basal diet (5 g lysine, 13 MJ DE/kg[C]), or basal diet + energy (maize starch + soya oil in 3:1 ratio [E]), or additional basal diet supplying both protein and energy [P]. Lactation diets provided either high (180 g CP/kg, 9g lysine/kg [H]) or low lysine (120 g CP/kg, 6g lysine/kg [L]) and were formulated to be isoenergetic (14.5 MJ DE/kg) and fed to appetite. From day 21 of lactation, sows were separated from their litters and housed next to a boar for 8 hours each day; final weaning occurred on day 31.
Sow productivity is a major objective for genetic improvement of pigs. Research in Europe and the USA has indicated the greater reproductive rate, but lower growth rate and leanness of several Chinese genotypes, including Meishan (Haley, Lee and Ritchie 1995, Young 1998). To better assess the potential of Meishan genes Cotswold has developed a ½ Meishan ½ Landrace synthetic female grandparent line selected for leanness and litter size for seven generations. To determine whether selection in this line has exploited the advantages of Meishan whilst limiting the disadvantages the genetic gains in growth and reproductive performance were estimated. Also progeny of a ¼ Meishan crossbred parent gilt (½ Meishan × Large White) were compared to European type crossbred pigs containing no Meishan genes.
Feed restriction prior to slaughter may reduce live and carcass weight gain (Murray and Jones, 1994) and meat quality (Warriss, 1982) but can reduce carcass contamination and the amount of waste to be disposed of at the slaughter house (Eikelenbloom et al., 1991). Most literature studies are however based on a single feed restriction while group housed pigs may be slaughtered over a period of time and can therefore be subjected to several periods of feed restriction. This study was conducted to examine the effects of feed restriction prior to slaughter on the production performance and meat quality of group housed finishing pigs.
There were three experimental treatments (1) control - ad libitum access up to point of transport, feeders closed off for 12 hours (Treatment 2) and feeders closed off for 20 hours (Treatment 3) prior to transport to the slaughter house. All pigs had unrestricted access to water. Four hundred and eighty six, 35 kg crossbred pigs, housed in groups of 18, were randomly allocated to 9 replicates of the three treatments. Pigs were slaughtered when a target live weight of 102 kg was reached. Production performance was recorded on a weekly basis when the first pig in any treatment approached 95 kg live weight until all pigs were slaughtered.
The tenderness of pork is one of the most important quality attributes to the consumer. Since it is very time-consuming and costly to evaluate tenderness by taste panel, Warner-Bratzler shear force (WBSF) is often used as a measure for meat tenderness (Boccard et al., 1981). However, the WBSF method gives a value for the maximal force needed to shear a cylindrical core of cooked meat, while the tenderness perception by the consumer is a result of the biting and chewing experience of grilled or fried meat. Moreover, this method is originally designed for the assessment of beef tenderness. The objective of this study was to evaluate modifications to the WBSF method to improve the correlation with pork tenderness.
A number of welfare and production problems are associated with weaning piglets including belly-nosing, ear and tail-biting, depressed immune responses, low intake of pelleted feed and impaired growth rate. These problems are, however, less pronounced in piglets reared on outdoor systems, which initially consume more pelleted food and show less belly-nosing and ear and tail biting than comparable indoor reared piglets. The objective of this study was to investigate how these differences in post weaning behaviour relate to the piglets' pre-weaning behaviour in the two rearing environments.
The study was carried out on a 200 sow breeding herd (Camborough line 12) with sows equally divided between extensive and intensive systems. In the intensive system, sows were singly housed prior to farrowing in crates and their piglets received a pelleted “creep” feed prior to weaning. On the outdoor system, sows were allowed to build straw nests in arks for farrowing and both sow and piglets had access to pasture. Each ark had observation holes in the front and back to allow sampling of the piglet's behaviour without disturbing the sow. Indoor and outdoor piglets were weaned at three weeks of age and mixed together in groups of 90-120 in straw-yard housing with access to a pelleted feed.
The mixing of unfamiliar sows at weaning results in the establishment of dominance hierarchies, frequently involving aggression. In commercial situations, with limited available flight distances, this can result in injuries and poor sow welfare. The objectives of this study were to measure flight and chase distances, and the incidence of aggressive interactions and levels of skin damage that occur when newly weaned sows were mixed in a large area where flight and chase distances were unlikely to be limiting.
Eight replicate groups of six unfamiliar sows were mixed in an arena (18x10.5m) at weaning. The sows were mixed at 09.00 h on Day 1, removed on Day 2 at 08.00 h for feeding in individual stalls, and returned to the arena at 09.00 h. Sows were observed directly from 09.00 h to 16.00 h on Day 1, and from 09.00 h to 13.00 h on Day 2. Video tape records were taken continuously for 28 hours from 09.00 h on Day 1. All aggressive interactions were recorded and categorised into three classes: brief (single knock, snap or bite), one-sided fight (no retaliation by defender), or two-sided fight (defender retaliates).
Cadmium (Cd) is a non-essential toxic heavy metal which is added to soil in phosphorous fertilizers and sewage sludge. Cd enters the human food chain via animals fed on crops from these soils, food of vegetable origin and smoking. In chronic exposure situations Cd accumulates in the liver and kidney of animals and man. Intake resulting in a Cd concentration of over 200μg/g wet weight in the kidney cortex results in kidney damage in humans (Friberg et al., 1974). With the prohibition of disposal of sewage sludge at sea in 1998, it is likely that more Cd will be deposited on soils. Current limits for Cd in animal feed are intended to prevent food from animal origin from exceeding legal Cd limits. This work examines the behaviour of Cd in the ovine body and models organ Cd from given intakes to investigate whether current limits in feed are safe and result in animal products fit for human consumption.
In previous studies (Mylne et al, 1992; McKelvey et al, 1997)) we have shown that the recovery of sheep embryos via the cervix can be facilitated by combining topical application of prostaglandin E2 (PGE2) to the external os cervix with systemic oestradiol treatment (E2) to dilate the cervix. The combined PGE2 and E2 treatment did not inhibit early embryo development (McEvoy et al, 1996) but conceptus viability was not determined. The objective of the present study was to test the viability of embryos recovered transcervically following dilation of the cervix with exogenous hormones and provide quantative data on their subsequent ability to establish normal pregnancies.
The periparturient relaxation (PPR) in acquired immunity in ewes has been ascribed to various factors, including poor nutrition (Barger, 1993). Clinically, the faecal egg count (FEC) may increase during PPR when the ewe is continuously infected with gastrointestinal parasites. As such, the periparturient ewe plays an important role in the epidemiology of parasitic infections. The nutritional basis of PPR probably includes metabolizable protein (MP), since host's responses, in terms of immunity and resilience, are highly proteinaceous by nature. We propose that the PPR directly results from less MP being available to maintain acquired immunity and resilience, since an increasing amount of MP is directed to bodily functions with higher priority (reproduction). It is hypothesized that the increased FEC in the parasitized periparturient ewe reduces if her MP-intake exceeds her assumed MP-requirement (AFRC, 1993).
The deposition of dung on pasture may create a trade-off between the benefit of increased nutrient intake due to the leaching of nutrients and the risk of parasitism due to migration of helminth parasite larvae (Sykes, 1987), from the faeces to the sward. Physiological state can affect herbivore foraging decisions in relation to this trade-off. Our objectives were to determine whether such a trade-off exists in a grazing situation for sheep and whether level of feeding motivation and parasitic status affect the grazing behaviour of sheep faced with this trade-off.
Texel x Greyface lambs were presented pairs of swards (36 x 21cm) which varied in nitrogen content (high=N+; low=N-) and level of contamination with faeces from sheep infected with Ostertagia circumcincta (Ost.) (20g faeces per sward=F+; no faeces=F-) and allowed to graze for short periods (60 bites or ten minutes). We defined ‘taking the trade-off’ as taking more bites from an N+F+ sward compared to an N-F- sward, when presented together as a choice.
The UK Metabolisable Protein (MP) system (AFRC, 1993) assumes that MP intake is converted to milk net protein with an efficiency of 0.68 and that MP for maintenance is 2.30*liveweight0.75. Previous work has indicated that the efficiency of MP use for milk production may be too high or that the amount of MP required for maintenance may be too low (Newbold et al, 1994). This experiment was designed to investigate the relationship between MP supply and net protein output in diets of differing MP to Metabolisable Energy (ME) ratios.
Four‘cornerstone’ diets based on grass and maize silage (0.33:0.67 dry matter basis), were formulated to meet ME requirements and either 0.25 above or below MP requirements for either 46 or 24 kg milk/d. A total of 72 multiparous Holstein cows, on average 46 days post calving at the start of the study, were grouped into blocks of 4 cows on the basis of milk energy output in the covariance period. ME and MP requirements for each block of cows were calculated from milk energy and milk protein yield in the covariance period.
To satisfy the increased nutrient requirements of high genetic merit dairy cows, diets of increased nutrient density and intake potential are required. This can be achieved through increasing the feed value of the forage component of the diet (grass silage or grazed grass) and by increasing concentrate feed levels. However both approaches tend to reduce the fibre concentration of the diet, and the physical effectiveness of the fibre in terms of its ability to stimulate ruminal processes. The incorporation of small quantities of straw into the diet has been suggested as a means of overcoming this problem and hence improving animal performance. This study was undertaken to examine the production response by dairy cows to straw inclusion in high quality grass silage and zero grazed grass diets.