The number of cells in bovine and ovine embryos is reduced when steer serum which can generate high concentrations of ammonia in vitro is included in the culture system (Kuran et al., 1998). Moreover, production of embryos in synthetic oviduct fluid (SOF) medium supplemented with this serum causes fetal oversize (Sinclair et al., 1998). The present study investigated the effect of the same high ammonia-producing steer serum in a two-phase culture system on bovine embryo development and blastocyst cell numbers.

The experimental design was a 2 x 2 factorial with 5 replicates and involved a total of 928 bovine oocytes that were matured and fertilized in vitro (IVF = Day 0). Presumptive zygotes were cultured in SOF supplemented with 10% v/v steer serum (SOF+SS; n=461) or with amino acids plus 0.4% w/v crystalline BSA (SOFaaBSA; n=467) for an initial period of 48 h following IVF.

Serum, which is routinely included in many embryo culture media, can decrease the viability of bovine and ovine embryos produced in cultures employing synthetic oviduct fluid (SOF; Kuran et al., 1999) and represents a possible route for transmission of disease. Alternative approaches include the use of chemically defined culture media but results from studies which avoid sera and its derivatives (e.g., albumin) are generally less favourable due to a lack of knowledge regarding the embryo's response to specific nutrients, most notably fatty acids. As a preliminary step towards investigating fatty acid influences on bovine embryo development in vitro, the present study examined the effect of adding palmitic acid (C16:0) to SOF plus bovine serum albumin (BSA) on the performance of this semi-defined culture medium and contrasted it with embryo production in SOF supplemented with serum.

Insemination at an inappropriate time is one of many constraints to good fertility in dairy cows. As a result, many studies have attempted to improve the synchrony of oestrus in controlled breeding programmes. However, the success of insemination depends not merely on the detection of oestrus, but also on the timing of ovulation relative to insemination. Thus a better understanding of the factors associated with the precise timing of behavioural oestrus and ovulation is required. In this study the time of ovulation has been determined, by ultrasound scanning, in relation to a variety of follicular phase events in dairy cows following both natural luteolysis and luteolysis induced by treatment with a prostaglandin F2a analogue. The objectives were firstly to determine whether differences existed in the timing of follicular phase events following natural and induced luteal regression and secondly to determine the degree of variation that exists between the timing of ovulation and the timing of other follicular phase events.

Historically there has been some controversy over possible detrimental effects of exogenous prostaglandin F? ? ? (PGF? ?) administration on the function of the subsequent corpus luteum (CL). In the light of recent evidence that early luteal phase progesterone is essential for embryonic development (Mann et al., 1996) combined with the clinical use of PGF2? analogues in herd fertility management, an urgent need has arisen for this matter to be clarified. This abstract presents work designed to investigate whether two of the commercially available PGF? ? analogues used in veterinary therapy have any detrimental effect on corpus luteum function.

The importance of falling progesterone (P4) concentrations in the initiation of parturition and the onset of lactogenesis in many species has long been recognised (Thorburn, et al., 1972). O'Doherty and Crosby (1996) reported a negative linear relationship between P4 concentration at 1 hour post lambing and colostrum yield at 1 h and total yield at 18 h. The administration of progesterone failed to delay parturition when given at a daily dose of 80 mg for a week but larger doses of progesterone (160 mg/day) blocked term labour in most sheep (Bengtsson and Schofield, 1963). The objective of this experiment was to examine the effects of exogenous progesterone administration to ewes in late pregnancy on ewe serum progesterone concentrations, gestation length and colostrum yield and quality.

The mid-gestation peak in activity of the fetal gonadotrophic axis is thought to be crucial for normal reproductive development. It is clear that the increase to mid-gestation is a result of the concomitant rise in gonadotrophs (Thomas et al., 1993). The mechanisms responsible for the decrease after mid-gestation are unclear, but may involve feedback from the placental steroids (Challis et al., 1981; Gluckman et al., 1983). The aim was to determine the roles of the placental steroids, progesterone and oestradiol, in the late-gestation decline in fetal gonadotrophins using the oestradiol antagonist ICI 182,780 and the progesterone antagonist RU486.

Feeding diets high in fibre to breeding sows has been found to have a positive effect on reproductive performance. Danske Slagterier (1994) found a significant increase in litter size when sows were fed a diet containing high levels of unmolassed sugar beet pulp (USBP) during pregnancy and lactation. Litter size is influenced by two main factors; ovulation rate and embryo survival. Glasgow et al (1996) found no increase in ovulation rate in gilts fed high USBP diets. This experiment was designed to assess the effect of feeding a high USBP diet on endocrinology and early embryo viability.

The experiment was of a randomised block design incorporating two diets; a cereal based diet (C) and a diet containing 50% unmolassed sugar beet (HF). 72 gilts of lean genotype (Newsham Hybrids) were allocated to treament at 138 days of age, housed in groups of 6 and had liveweight and backfat thickness recorded fortnightly. For the first 8 weeks, HF gilts were fed ad-libitum and C gilts were pair fed to the same daily energy intake. Subsequently, gilts were floor fed isoenergetically at a flat rate of 2.8 kg/d (HF) and 2.3 kg/d (C).

A number of studies have shown that milk urea levels above about 350 mg/l are associated with reduced fertility in dairy cows (Ropstad and Refsdal, 1987; Gustafsson and Carlsson, 1993). A significant and increasing proportion of UK milk producers receive regular information on the urea content of bulk milk as part of routine milk testing. Two studies were undertaken to examine whether the urea content in bulk milk (Study 1) or in milk from individual cows at about the time of service (Study 2) could be used as a management aid to improve fertility status.

In Study 1, the milk urea (MU) contents in bulk milk samples from 475 farms in England and Wales were determined by NIRS. Fertility data for each farm was obtained from National Milk Records. Analysis of the data for each month of the study was restricted to those herds in which ≥15 cows were served.

Rosa and Bryant (1997) have described how sexual experience increased the amount of time that rams spent in courtship of seasonally anoestrous ewes. There was a non-significant trend for a greater proportion of ewes to respond to increased ram stimulation in early July, indicating that efforts to enhance the cues provided by rams at this time may be effective in increasing the incidence of ovulation. The objective of this experiment was to establish if advancing the seasonal changes associated with the rams by treatment with exogenous melatonin and allowing the rams prior sexual experience would induce ovulation in anoestrous ewes in early July.

Previous work conducted with fermented whole crop wheat (WCW) silage has focussed on the effects that stage of maturity can have on nutritive value and milk production (Sinclair and Wilkinson 1998, Phipps et al. 1998). An alternative means of manipulating the nutritive value of WCW is to alter the relative proportion of straw to grain through altering cutting height at harvest. Additionally, the form of energy supplied by the concentrate also offers the potential of manipulating milk production in cows fed diets containing WCW. The objectives of the current experiment were therefore to determine the effect of two cutting heights at harvest and supplement type on the performance of dairy cows offered fermented WCW silage.

Previous work with fermented whole crop wheat (WCW) silage has focussed on the effects of stage of maturity on nutritive value and milk production (Sinclair and Wilkinson 1998). An alternative means of manipulating nutritive value may be to alter the relative proportions of grain to straw by changing the cutting height at harvest. The objectives of the current experiment were to determine the effects of two cutting heights on the aerobic stability and whole tract digestibility of fermented WCW silage offered to sheep.

Winter wheat (variety Hunter) was grown as a conventional crop and harvested at a dry matter (DM) content of 450 g/kg and a Zadock growth stage of approximately 85 (soft dough). The crop was cut to leave a stubble length of either 17.9 cm (long straw, LS) or 38.2 cm (short straw, SS) prior to ensiling in separate ag-bags.

Whole crop wheat (WCW) silage is potentially an important complementary forage to grass silage grown in the UK and recent studies suggest that although partial replacement of grass silage with either urea treated or fermented WCW increases forage intakes, responses in terms of milk yield and composition are poor. For urea treated WCW this has been attributed to the fact that mature intact grains are poorly digested in the rumen. (Abdulla et al. (1996). However, the rumen degradation characteristics of fermented WCW are unclear. The objective of this experiment was to investigate the effect of crop maturity (Mat) and endosperm type (Endo) on the in situ dry matter (DM) degradability characteristics of fermented WCW silage.

The efficiency of nitrogen (N) utilisation in dairy cows fed grass silage diets is normally low and is related to an impaired utilisation of N in the rumen. Choice of carbohydrate type may affect this efficiency, influencing milk production and composition, and changing the output of N in faeces or urine. This experiment was undertaken to examine the effect of different iso-energetic supplements containing contrasting energy sources on N utilisation and milk production in early/mid lactation dairy cows fed early cut partially wilted grass silage.

Six iso-energetic supplements were formulated as treatments; four to contain 160 g CP/kg DM and contrasting carbohydrate sources, viz.: neutral detergent fibre (NDF; wheatfeed, 350 g/kg, molassed and unmolassed sugar beet pulp 412 g/kg); low degradability starch (LDS; maize grain 500 g/kg, wheat 237 g/kg); high degradability starch (HDS; wheat and barley grain 812 g/kg); and soluble sugars (SS; molasses, 525 g/kg, citrus pulp, 125 g/kg).

Feeding of highly fermentable carbohydrates is often necessary to meet the energy requirements of high producing cows. Unfortunately, these diets can lead to reduced rumen pH and impaired productivity. Earlier work showed that maize silage intake was greatly reduced when concentrates producing a high rumen acid load (Acidogenicity Value (AV); Wadhwa et al., 1998) were included at 0.5 of feed DM intake (Dewhurst et al., 1998). This further experiment sought to define the level of concentrate feeding at which AV becomes important.

Sixteen Holstein-Friesian cows in the third month of lactation were used. After a covariance period, cows went onto a cyclical changeover design with four periods each lasting for 21 days. Maize silage was offered ad libitum, through Calan gates, along with a fixed allocation of one of 8 concentrates.

High concentrate feed levels, with a consequent fall in the fibre content of the diet, are increasingly being offered to high genetic merit dairy cows. To improve fibre intake, small quantities of straw are often incorporated into the diet. This study was undertaken to examine the production response of dairy cows, offered a medium quality grass silage based diet together with relatively high levels of concentrate supplementation, to straw inclusion in the diet.

Forty high genetic merit dairy cows, 20 multiparious and 20 first lactation animals (PTA95 fat + protein = 41.4 and 39.7 kg respectively) were used in this study. The study consisted of four treatments, arranged in a two period (4 week duration), partially balanced change-over design trial, with first lactation and multiparious animals being blocked separately. The experimental treatments consisted of grass silage mixed with one of four levels of straw, and offered ad libitum in the form of a mixed diet.

In a previous short term study, Ferris et al. (1997) demonstrated that similar levels of nutrient intake and animal performance could be obtained by either increasing silage feed value and reducing concentrate feed level, or by reducing silage feed value and increasing concentrate feed level. The principles established in this study were incorporated into this trial to examine two systems of milk production over a full lactation, including both the winter and grazing periods.

Forty high genetic merit dairy cows (PTA95 fat + protein = 38.2 kg), in their second or subsequent lactation, were used in a continuous design full lactation study. Animals had a mean calving date of 1 November and were allocated to one of two systems of milk production, HF or HC, within 36 hours of calving. During the winter, animals on system HF were offered a silage with high feed value characteristics, supplemented with 5.5 kg of concentrate (crude protein concentration of 280 g/kg DM) through an out-of-parlour feeding system.

Previous studies have shown that the timing of supplement distribution and supplement type can have implications on forage intake and/or production. For example, Robinson et al. (1997) showed that feeding a protein supplement at 00.30 h compared with 08.30 h increased fat yield through stimulation of rumen fermentation. The objective of the present trial was to test the hypothesis “that supplying a protein supplement either before or after silage was offered would affect feeding pattern and silage intake”.

Twelve multiparous cows, with average starting milk yield of 25.4 (s.d. 5.95) kg/day were allocated to one of six treatments in an incomplete Latin square with four periods of 21 days. Grass silage (219 g/kg DM, 151 g CP/kg DM) was fed ad libitum mixed with barley in the ratio 3:1 on a DM basis.

In the Netherlands, grass and forage maize are the most important fodder crops. However, on drought prone sandy soils, and in years with insufficient rainfall the yield of maize is very low (7 to 8 tons DM/ha). Therefore, sprinkle irrigation is often applied to overcome problems with drought. However, in some regions sprinkle irrigation is not possible because of a lack of suitable water or due to legislative restrictions on the use of water for irrigation. In situations where water is a limiting factor for growing maize, triticale may be an alternative fodder crop. Triticale grows mainly during the early spring when there usually is a precipitation surplus and so, water is not a limiting factor for growth. When triticale is harvested as triticale whole crop silage the DM yield ranges between 9 and 11 ton of dry matter per hectare. Therefore, under water limiting conditions it may be attractive to replace forage maize by triticale whole crop silage.

Higher dry matter intakes (DMI) have been reported in dairy cows fed maize silage than in dairy cows fed grass silage. The objective of this experiment was to investigate this phenomenon by the measurement of digestibility and the determination of rumen outflow rates for both forages. The response in milk production of late lactation dairy cows to grass or maize silage was also measured.

Fourteen late lactation multiparous dairy cows (n = 7) were fed diets containing either grass silage (GS) (DM: 197g/kg; pH: 4.05; NDF: 642g/kg DM) or high starch maize silage (MS) (DM: 339g/kg; pH: 3.94; starch: 360g/kg DM; NDF: 442g/kg DM) ad-libitum plus 4kgs/hd/day of a dairy concentrate (233g CP/kg DM). Urea (460g N/kg DM) was used as a source of degradable protein (10g/kg DM) for the MS diet which also included straw (40g/kg DM). Dietary NDF equalled 542 and 423g/kg DM for the GS and MS diet.

The production and utilization of complementary cereal/legume bi-crops as ruminant feeds is beneficial for several reasons. The nitrogen fixation by the legume reduces the amount of fertilizer nitrogen required by the cereal. The cereal in turn supports the legume, thereby preventing the lodging that typifies pure stands of mature forage peas. When bi-crops are fed, the legume and cereal components respectively provide relatively low cost protein and energy, which may be synchronously supplied to the animal. In Denmark, pea-barley bi-crops are reported to reduce the cost of feeding without reducing intake and animal performance (Kristensen, 1992). However, little is known about the intake potential and level of animal performance sustainable from such bi-crops when produced and fed under UK conditions. Therefore this study determined the intake, in vivo digestibility and nitrogen (N) balance in sheep of spring sown, peawheat bi-crop silages harvested at three stages of maturity.