Significance of quality of truly digestible protein on performance of ewes at late pregnancy and early lactation

Two trials were conducted in ewes at late pregnancy and early lactation in order to evaluate the effects of substituting the moderate degradable protein of soy bean (SBM), with a low degradable protein of corn gluten meal (CGM), accordingly that both diets were calculated to provide equal truly digestible protein (PDI). At the first trial thirty multiparous ewes were examined in an 8-week study that started at parturition. Animals were fed in groups (15 ewes), with two isocaloric-isonitrogenous-isofibrous rations. Treatments were: (A) SBM, (B) CGM. Diets were different at PDIA/PDI ratio (0.52 versus 0.63). The second trial lasted 7 weeks, 5 weeks pre partum till 2 weeks post partum. Three rations were tested by the use of 48 pregnant ewes. Ewes were allotted to three equivalent groups: (A) SBM and wheat bran, (B) CGM and corn gluten feed, (C) CGM and corn gluten feed plus additional lysine (CGML). Data from both trials were analyzed as repeated measures. CGM compared to SBM decreased milk yield and fat corrected milk (FCM) yield (2.25 and 1.98 kg of milk; 2.47 and 2.17 kg of FCM), while tended to decrease milk's protein content (5.45 and 5.36%, for the SBM and CGM group). The daily production of fat, protein and lactose were higher in SBM than in CGM. CGM ration decreased body weight (BW) gain of ewes during late pregnancy and mean birth BW of litter, and also caused a 30% increase of abortions-dead births. CGM cannot totally replace SBM, in ewes' diets at early lactation, because of the decrease in milk yield as well as the milk's protein content, even when equal PDI is provided, due to low lysine content. This trial has extended the knowledge from cattle, that supplementation of lysine, usually the first limiting amino acid, is also crucial in ewes during pregnancy and lactation.