ABSTRACT
This study was conducted to evaluate changes in productive performance, in terms of milk yield and its composition, of lactating goats, resulted of feeding two rations differ in R : C ratio, and supplemented with or without Rumi yeast (RY) supplementation. Twenty-four lactating goats, in their 2nd -3rd season of lactation, with an average age of 24-30 months, and average body weight 35.83±0. 5 kg were distributed according to their live body weight and milk production into four similar groups, (6 goats each). The experiment lasted for 120 days after the does weaned their offspring.
The first two groups, low roughage, were fed 30% (CS) and 70% (CFM). R1 group supplemented with 3g RYS/head/day, while R2 was without RY. The other two groups, high roughage, fed 70% CS and 30% CFM, R3 with 3g RY/head/day and R4 without RY.
The obtained results showed that daily milk and fat corrected milk (4% FCM) yields were significantly (P<0.05) increased with R1 and R2 (high concentrate, HC) than those of R3 and R4 (high roughage, HR). Meanwhile, milk yield was significantly (P<0.05) higher with groups supplemented with RY than unsupplemented ones. Averages of DM, TDN and DCP intakes were the highest with R1, compared with the other tested rations. The groups fed HC rations with or without RY had higher conversion rate of feed to milk (0.70 and 0.60 kg milk yield/kg DMI, for R1 and R2, respectively) compared to those fed HR rations, with or without RY. The best feed conversion efficiency values expressed as (kg DCP/ kg milk) were recorded with R1 and R3, being 6.77 and 6.41 kg DCP/kg milk, respectively. Economic feed efficiency (EFE) was the best for goats fed HR supplemented with RY (R2) (165.67%). The results of blood parameters showed that groups fed R2 and R4 (URY) recorded significantly (P<0.05) higher values of total protein, albumin and globulin, compared with those fed R1 and R3 (rations with RY). Yeast supplementation slightly increased glucose, cholesterol, triglyceride and urea concentrations in blood plasma of goats.
It could be concluded that supplementation of Rumi live yeast (RLY) at the level of 3g head/day to rations of lactating goats either with HC or HR markedly improve milk yield, milk composition and feed conversion to milk efficiency. The goats fed HR supplemented with RY (R3) had better economic feed efficiency (EFE) than those fed other tested rations. No interactions between yeast supplementation and dietary roughage: concentrate ratio were recorded.