The influence of extruding corn grain in diets fed to Finn × Awassi crossbred ewes during late pregnancy on birth weight of lambs

Abstract

As part of a program aimed at increasing lamb survival by maximizing lamb birth weight, the relationship between corn starch degradability in late pregnancy diets and lambing performance was studied in 60 Finn–Awassi ewes fed diets supplemented with 500 g d−1 of whole (WC), extruded (EC) or ground corn (GC). Lamb birth- weights ranked as follows: single lambs: EC > WC > GC (NS at 2nd parity, P < 0.10 at 3rd and higher parities); twin lambs: EC > WC = GC (P < 0.02 at 2nd, P < 0.07 at 3rd and higher parities). The ratio between birth weight of twin lamb litters and maternal weight measured 4 d postpartum in ewes at 3rd and higher parities was 25% greater in EC-fed ewes than in their WC- or GC-fed counterparts (P < 0.03). Colostrum accumulation prepartum was not affected by litter size or diet, but was higher (P < 0.04) in ewes from 3rd and higher parities compared with 2nd parity. Plasma NEFA (positive correlation) and insulin (negative correlation) concentrations on day 23 pre-partum, or plasma NEFA (positive correlation), insulin and glucose (negative correlations) concentrations on day 9 pre-partum, and ewe body weight at day 4 post-partum (positive correlation) explained 78% of variance in lamb birth weight (P < 0.0001). In conclusion 1) in prolific ewes at late pregnancy, highly degradable corn starch promotes better fetal growth than moderately degradable corn starch; 2) the positive correlation between NEFA and lamb birth weight, even in "overfed" ewes carrying single lambs indicates that maximal lamb birth weight is not likely to be maximized without some degree of maternal lipolysis. Key words: Sheep, birth weight, pregnancy, nutrition, starch, prolificacy