β-Casomorphin is an opioid-like bioactive peptide derived from β-casein of milk that plays a crucial role in modulating animal’s feed intake, growth, nutrient utilization and immunity. However, the effect of β-casomorphin on lipid metabolism in chickens and its mechanism remain unclear. The aim of this study was to investigate the effects of β-casomorphin on fat deposition in broiler chickens and explore its mechanism of action. A total of 120 21-day-old Arbor Acres male broilers (747.94±8.85 g) was chosen and randomly divided into four groups with six replicates of five birds per replicate. Three groups of broilers were injected with 0.1, 0.5 or 1.0 mg/kg BW of β-casomorphin in 1 ml saline for 7 days, whereas the control group received 1 ml saline only. The results showed that subcutaneous administration of β-casomorphin to broiler chickens increased average daily gain, average daily feed intake and fat deposition, and decreased feed : gain ratio (P<0.05). The activity of malate dehydrogenase in the pectoral muscle, liver and abdominal adipose tissue was also increased along with the concentrations of insulin, very-low-density lipoprotein and triglyceride in the plasma (P<0.05). The activity of hormone-sensitive lipase in the liver and abdominal adipose tissue and the concentration of glucagon in the plasma were decreased by injection with β-casomorphin (P<0.05). Affymetrix gene chip analysis revealed that administering 1.0 mg/kg BW β-casomorphin caused differential expression of 168 genes in the liver with a minimum of fourfold difference. Of those, 37 genes are directly involved in lipid metabolism with 18 up-regulated genes such as very low density lipoprotein receptor gene and fatty acid synthase gene, and 19 down-regulated genes such as lipoprotein lipase gene and low density lipoprotein receptor gene. In conclusion, β-casomorphin increased growth performance and fat deposition of broilers. Regulation of fat deposition by β-casomorphin appears to take place through changes in hormone secretion and enzyme activities by controlling the gene expression of lipid metabolism and feed intake, increasing fat synthesis and deposition.

Fertility is an important component of herd production efficiency, as each additional oestrous cycle that does not result in a planned pregnancy adds to the cost of dairy farming. In addition to the negative impact on milk production, the high costs of veterinary intervention, re-insemination and herd replacement, subfertility can affect the rate of genetic gain in traits of economic merit. In contrast with the steady increase in average milk yield per cow during the last 30 years, there has been a decline in conception rate to artificial insemination in both the USA and in the UK.

The genetic correlation between yield and fertility has been equivocal. Attempts to improve the reproductive efficiency in dairy cattle through breeding and selection have been frustrated to date by the lack of heritable reproductive parameters conducive to high fertility. However, the traditional fertility parameters of interval to first service, services per conception, days open and calving intervals are highly influenced by managerial decisions and have, as expected, heritabilities too low to permit a meaningful genetic gain through selection. An alternative approach is to use the growing body of evidence that the majority of endocrine factors affecting reproduction are a result of gene expression at the hypothalamic, pituitary, ovarian or uterine level. Mechanisms such as commencement of post-partum cyclicity, follicle wave patterns, manifestation of oestrus, luteal competence and level of embryo mortality are appropriate for study. Research is required to investigate the genetic component of the variation between animals in these parameters, their phenotypic and genetic correlations with fertility and their association with other production traits.

In summary: (a) subfertility is a syndrome with multiple causes and only the symptom in common; (b) improvement in fertility will continue to be frustrated until recorded traits provide more accurate estimates of breeding values; (c) techniques are now available to estimate the genetic variation in physiological components conducive to improved reproductive efficiency; (d) once the heritable components of fertility are identified, these tools could be introduced into progeny testing and breeding nuclei, from which the genetic improvement can be widely disseminated. Selection for those components with sufficient genetic variation will result in the improvement of the integral endocrine and other physiological mechanisms favourably correlated with high fertility (e) these tools may also assist in detecting quantitative trait loci for faster genetic gain through markers-assisted selection.

Patterns of milk production and circulating blood metabolite and hormone concentrations were determined throughout a 14-week lactation in groups of 10 twin-rearing East Friesland EF) and Scottish Blackface (SBF) ewes. All ewes were offered, ad libitum, a pelleted diet throughout the experiment and milk yields were measured weekly. Pooled blood samples (six samples, 20-min intervals), collected before feeding, on 1 day of each week, were assayed for plasma glucose, non-esterfied fatty acids, 3-hydroxybutyrate (3-OHB), albumin, total protein, insulin, growth hormone (GH), cortisol, prolactin, thyroxine (T4), and triiodothyronine (T3). At weeks 2, 4,10, and 14, samples were collected at 20-min intervals for 8 h and assayed individually for plasma insulin, GH, cortisol, and prolactin. Mean daily intakes and milk yields of ewes were similar in the two breeds. Mean pre-feeding concentrations of most blood metabolites during the experiment were also similar in ewes of the two breeds but SBF ewes had higher plasma concentrations of 3-OHB (0·67 v. 0·43 mmol/l; P < 0·01) and total protein (73·2 v. 66·4 g/l; P < 0·001). SBF ewes had higher overall mean concentrations of insulin (9·53 v. 4·36 mU/l; P < 0·001), cortisol (7·59 v. 573 μg/l; P < 0·05), prolactin (457·1 v. 316·1 μg/l; P < 0·05), and T3 (1.32 v. 1·12 μg/l; P < 0·001). GH and T4 profiles were similar in the two breeds. Following the daily introduction of fresh food, there were significant increases in concentration of insulin (P < 0·001) and cortisol (P < 0·01) while there was a decrease in mean concentrations of GH (P < 0·001) and prolactin (P < 0·01). There were significant interactions between breed and feeding effects on insulin, GH, cortisol and prolactin concentrations. Patterns of milk production in ewes of these breeds were associated with changes in insulimGH ratios both before and after feeding which may be of a causal nature.

Milk yields and blood metabolite and hormone profiles of a total of 40 Greyface ewes lambing in January or April and suckling single (S) or twin (T) lambs were determined. Ewes were given a fixed level of feeding throughout the first 10 weeks of lactation. Milk yields were measured weekly. Pooled blood samples (six samples; 20-min intervals), collected at weekly intervals for the first 10 weeks of lactation, were assayed for glucose, non-esterified fatty acids (NEVA), 3β-hydroxybutyrate, urea, albumin, total protein, insulin, growth hormone (GH), cortisol, prolactin, thyroxine (T4) and triiodothyronine (T3). At weeks 2, 4 and 10 of lactation samples were collected at 20-min intervals for 8 h and assayed individually for insulin, GH, cortisol and prolactin. Mean daily milk yield was lower in S than in T ewes in January (1·93 v. 2·33 kg/day; P < 0·05) and April-lambing ewes (1·95 v. 2·28 kg/day; P > 0·05). Profiles of NEFA and 3β-hydroxybutyrate indicated that T ewes were mobilizing adipose tissue at a greater rate than S ewes. The higher milk yield and rate of fat mobilization in T ewes compared with S ewes was associated with lower overall mean insulin concentrations (3·37 v. 5·04 mil per I; P < 0·002) and higher GH (6·29 v. 2·77 μg/l; P < 0·001) and cortisol (7·04 v. 3·64 μg/l; P < 0·001) concentrations in the weekly samples. Differences between rearing groups in mean concentrations of T4 and T3 were generally small and not significant. Mean prolactin concentrations were much lower in the January- than in the April-lambing ewes (73·7 v. 270·2 μ/l; P < 0·001) but this difference was not associated with a difference in milk yield. Substantial increases in insulin and GH concentrations generally followed feeding but the post-prandial profiles were dependent on stage of lactation; while GH concentrations increased following feeding at weeks 2 and 4 of lactation, there was generally a decline in post-prandial concentrations at week 10. It is concluded that the patterns of insulin and GH secretion during the hours following feeding may be an important determinant of the rate of tissue mobilization and milk yield in ewes subject to differences in demand for milk created by differences in litter sizes.