title: Effects of replacing grass silage with either maize silage or concentrates during late pregnancy on the performance of breeding ewes fed isonitrogenous diets.
abstract: A study was undertaken to investigate the performance of breeding ewes fed a range of forage and concentrate-based diets in late pregnancy, balanced for supply of metabolizable protein (MP). For the final 6 weeks before lambing, 104 twin-bearing multiparous ewes were offered one of four diets: ad libitum precision-chop grass silage + 0.55 kg/day concentrates (GS); ad libitum maize silage + 0.55 kg/day concentrates (MS); a 1 : 1 mixture (on a dry matter (DM) basis) of grass silage and maize silage fed ad libitum + 0.55 kg/day (GSMS); or 1.55 kg/day concentrates + 50 g/day chopped barley straw (C). The CP content of the concentrates was varied between treatments (157 to 296 g/kg DM) with the aim of achieving a daily intake of 130 g/day MP across all treatments. Compared with ewes fed GS, forage DM intake was higher (P < 0.05) in ewes fed MS (+0.21 kg/day) and GSMS (+0.16 kg/day), resulting in higher (P < 0.001) total DM intakes with these treatments. C ewes had the lowest total DM intake of all the treatments examined (P < 0.001). C ewes lost more live weight (LW; P < 0.001) and body condition score (BCS; P < 0.05) during the first 3 weeks of the study but there were no dietary effects on ewe LW or BCS thereafter. The incidence of dystocia was lower (P < 0.01) in C ewes compared with those offered silage-based diets (7.5% v. 37.4% ewes), and was higher (P < 0.01) in ewes fed MS compared with GS or GSMS (50.7%, 34.7% and 26.9%, respectively). There were no significant dietary effects on the plasma metabolite concentrations of ewes in late pregnancy, pre-weaning lamb mortality, weaned lamb output per ewe or on lamb growth rate. The results of this study demonstrate that both maize silage and all-concentrate diets can replace grass silage in pregnant ewe rations without impacting on performance, provided the supply of MP is non-limiting. The higher incidence of dystocia in ewes fed maize silage as the sole forage is a concern.
authors.affiliation: Agriculture Branch, Agri-food and Biosciences Institute (AFBI), Large Park, Hillsborough, Co. Down, Northern Ireland BT26 6DR, UK. Ronald.Annett@afbini.gov.uk
authors.forename: R W
authors.initials: RW
authors.lastname: Annett
authors.forename: A F
authors.initials: AF
authors.lastname: Carson
authors.forename: A W
authors.initials: AW
authors.lastname: Gordon
mesh_terms: D000821:Animal Feed / Q000032:analysis*; D000818:Animals; D019587:Dietary Supplements; D004420:Dystocia / Q000517:prevention & control / Q000662:veterinary*; D005260:Female; D016014:Linear Models; D006109:Poaceae / Q000737:chemistry; D011247:Pregnancy; D012756:Sheep / Q000254:growth & development*; D012757:Sheep Diseases / Q000517:prevention & control*; D012820:Silage / Q000032:analysis*; D003313:Zea mays / Q000737:chemistry*