The mammary gland is a dynamic organ that undergoes dramatic physiological adaptations during the transition from late pregnancy to lactation. Investigation of the molecular basis of mammary development and function will provide fundamental insights into tissue remodelling as well as a better understanding of milk production and mammary disease. This is important to livestock production systems and human health. Here we use RNA-seq to identify differences in gene expression in the ovine mammary gland between late pregnancy and lactation. Between late pregnancy (135 days of gestation ± 2.4 SD) and lactation (15 days post partum ± 1.27 SD) 13 % of genes in the sheep genome were differentially expressed in the ovine mammary gland. In late pregnancy, cell proliferation, beta-oxidation of fatty acids and translation were identified as key biological processes. During lactation, high levels of milk fat synthesis were mirrored by enrichment of genes associated with fatty acid biosynthesis, transport and lipogenesis. Protein processing in the endoplasmic reticulum was enriched during lactation, likely in support of active milk protein synthesis. Hormone and growth factor signalling and activation of signal transduction pathways, including the JAK-STAT and PPAR pathways, were also differently regulated, indicating key roles for these pathways in functional development of the ovine mammary gland. Changes in the expression of epigenetic regulators, particularly chromatin remodellers, indicate a possible role in coordinating the large-scale transcriptional changes that appear to be required to switch mammary processes from growth and development during late pregnancy to synthesis and secretion of milk during lactation. Coordinated transcriptional regulation of large numbers of genes is required to switch between mammary tissue establishment during late pregnancy, and activation and maintenance of milk production during lactation. Our findings indicate the remarkable plasticity of the mammary gland, and the coordinated regulation of multiple genes and pathways to begin milk production. Genes and pathways identified by the present study may be important for managing milk production and mammary development, and may inform studies of diseases affecting the mammary gland.

Triplet‐bearing ewes and their lambs have the potential to improve flock productivity however, the lack of robust information on optimal nutrition and management is limiting their performance. In comparison to twins, the triplet lamb is; lighter, more metabolically challenged, has lower body temperature, and receives less colostrum and milk which combined results in lower survival rates and weaning weights. While scientifically based management guidelines are available for singletons and twins, guidelines are generally lacking for triplets. Although there is some knowledge on the impacts of nutrition, further studies are required to examine the impacts of varying feeding regimens in pregnancy and lactation, across the body condition range. Characterising the impacts of shelter and other paddock factors, stocking rate, mob size and human intervention would also be of benefit. Future studies must be large enough to allow for evaluation of lamb survival and litter birth weight variation.

The productive performance of highly fecund ewes and their progeny on ryegrass-based swards is limited in late pregnancy and lactation. Alternative herbages, such as chicory, plantain and red and white clover, have the potential to improve performance levels. In the present study, 49 twin- and 42 triplet-bearing Romney composite ewes bred to either Suffolk or Romney rams were allocated to one of three nutritional treatments from Day 131 of pregnancy [19 twin ewes on a ryegrass–white clover sward mix (Rye/WC); 16 twin ewes on a plantain–ryegrass sward mix (Plant/Rye); 14 twin ewes on a chicory–plantain–red and white clover sward mix (Herb); 13 triplet ewes on Rye/WC; 16 triplet ewes on Plant/Rye; and 13 triplet ewes on Herb] and remained on these sward treatments with their lambs until 75 days after the midpoint of the lambing period (L75). Nutritional treatment had no effect (P > 0.05) on ewe liveweight, body condition score (BCS) or non-esterified fatty acid and ß-hydroxybutyrate concentrations on Day 145 of pregnancy. At L75, ewes on the Herb treatment sward were heavier than ewes on Plant/Rye (70.75 ± 1.31 v. 61.43 ± 1.28 kg, respectively) and had a higher BCS than ewes on either Plant/Rye or Rye/WC (2.7 ± 0.1, 2.2 ± 0.1 and 2.3 ± 0.1, respectively). Sire type and nutritional treatment had no affect (P > 0.05) on lamb birthweight or weight at L75. At L20, lambs born to ewes on the Herb sward treatment were heavier than those on the Rye/WC and Plant/Rye treatments (8.74 ± 0.23 v. 7.98 ± 0.23 and 7.79 ± 0.22 kg, respectively; P < 0.05). Neither birth rank, sire type nor ewe treatment had any effect (P > 0.05) on maximum heat production on a per kg liveweight basis or total heat production. Romney-sired lambs on the Herb sward treatment had higher (P < 0.05) survival rates than those on the Rye/WC sward treatment (97.8% v. 61.7%, respectively). However, no such relationship was observed in lambs born to Suffolk sires (79.8% v. 84.8%, respectively). The survival response resulted in greater (P < 0.05) total liveweight of Romney-sired lambs at L75 per ewe on the Herb nutritional treatment than on the Rye/WC treatment (61.6 ± 5.0 v. 36.7 ± 4.6 kg, respectively) a relationship not observed (P > 0.05) in Suffolk-sired lambs. In conclusion, the present study indicates that there is the potential to improve the productive performance of multiple-bearing ewes and their lambs by grazing on a Herb sward mix.

The high concentration of secondary branched wool follicles is a distinctive feature of the Merino sheep. At present, the molecular control of the development and branching of secondary wool follicles (SF) remains elusive. To reveal the potential genes associated with the development of hair follicles, we investigated the characteristics of prenatal and postnatal development of wool follicles, and the transcriptional expression profile in fetuses/lambs from dams under either maternal maintenance or sub-maintenance (75% maintenance) nutrition. The density of SF and the ratio of SF to primary wool follicles (PF) were reduced (p < 0.05) in fetuses from day 105 to 135 of gestation under sub-maintenance nutrition. Differentially expressed genes were enriched in the binding, single-organism process, cellular process, cell and cell part Gene Ontology (GO) functional categories and metabolism, apoptosis, and ribosome pathways. Four candidate genes, SFRP4, PITX1, BAMBI, and KRT16, which were involved in secondary wool follicles branching and development, were identified. Our results indicate that nutritional intervention imposed on pregnant ewes by short-term sub-maintenance nutrition could provide a strategy for the study of wool follicle development. Overall insight into the global gene expression associated with SF development can be used to investigate the underlying mechanisms of SF branching in Merino sheep.

This study aimed to investigate the effects of ewe body condition score and nutrition on twin-bearing ewes and their offspring. At maximum Day 112 of pregnancy (range 96–112 days), 185 twin-bearing ewes were allocated to either a ‘Medium’ or ‘ad libitum’ (Adlib) feeding treatment for the following 25 days (P112–P136). Each feeding treatment included ewes of body condition score: 2.0 (CS2.0, Medium n = 32, Adlib n = 28), CS2.5 (Medium n = 31, Adlib n = 33) or CS3.0 (Medium n = 30, Adlib n = 31). After P136 ewes were offered Adlib feeding conditions. Medium treatment ewes were lighter (P < 0.05) than Adlib ewes at P136 and P142 and displayed lower (P < 0.05) body condition score at P136 and back-fat depths at P142. CS2.0 ewes had lower (P < 0.05) liveweights and body condition score at P112, P136 and P142 than CS2.5 ewes, which in turn had lower (P < 0.05) liveweight and body condition scores than CS3.0 ewes. Ewe feeding treatment had no effect (P > 0.05) on lamb liveweight or apparent colostrum intake. Ewe body condition score had no effect (P > 0.05) on lamb birthweight or apparent colostrum intake. Lambs born to CS2.0 ewes had greater (P < 0.05) survival than lambs born to CS2.5 ewes. At the end of the study lambs born to CS2.0 ewes were lighter (P < 0.05) than those born to CS2.5 and CS3.0 ewes although, there was (P > 0.05) no effect of condition score on total litter liveweight. In conclusion, these results suggest twin-bearing ewes of body condition 2.0–3.0 can be offered restricted feeding levels to at least Day 136 of pregnancy with few implications for their lambs.