EFFECT OF ENERGY SUPPLY ON MILK PRODUCTION AND MILK COMPOSITION OF DAIRY EWES

Abstract

During the cycle of reproduction, the lactating animal faced succesively of underfeeding and overfeeding. Two trials were done to evaluate the effect of energy supply on milk production and milk composition of dairy ewes. The first Trial (TI) was done to evaluate the effect of long term (2 months) underfeeding, while in the second trial (TII) mid-term (1 month) alternate effects of underfeeding and/or refeeding. Each trial was divided in two periods (P1 and P2) of one month (Pl : 28 days) and P2 (27 days). For each trial, mature Lacaune dairy ewes at mean lactation stages of 41 days (TI : n=18) and 48 days (TII 1 n=24) were allocated in one of two groups of feeding level (H: High or L : Low). Total Energy Requirement (TER) based on INRA recommendation (INRA, 1988) in TI was respectively for group H : 93 and 94% (Pl and P2) and for group L : 78 and 80%TER (P1 and P2), while in TII, animal in group H received 104 and 106 %TER (P1 and P2) compared to 83 and 86 %TER (Pl and P2) for group L. For both trials and for both groups, protein supply was 100%
covered according to INRA recommendation. Ewes were machine milked twice a day at 8.30 am and 5.30 pm. Milk recordings were done twice a week on two successive morning and evening milkings. Milk samples were taken to be analysed for fat and protein content. Statistical analysis of all data collected was conducted with the GLM procedure of SAS (1988). Results of these trials indicated that energy supply directly altered milk yield. During the first period, between diet H and L, milk loss was of 20% in TI from initial milk yield of 2.46 liters/head/day and 17% in Tll from initial milk yield of 2.16 liters/head/day. In the second periods respective differences were -31% (Tl) and -14% (TII). Inversion of energy supply for the same animal (in the second period of TII) from L to H or from H to L altered significantly the evolution of milk yield. Overfeeding stimulate the better persistency. Effect of energy supply on milk fat and protein content was not significant among the groups. In conclusion, energy supply either for mid-term (1 month) or for long-term period (2 months) alter significantly milk yield evolution without significant effect on milk composition of lactating dairy ewes.