The effect of altering the hay to concentrate ratio and concentrate composition on the rumen fermentation of dry sheep and milk production of lactating dairy ewes

In order to examine the effects of diets, with two hay to concentrate ratios and two forms of concentrates on the rumen fermentation of dry sheep and milk production of lactating ewes, three trials were conducted. In the first trial, four wether sheep, each fitted with a rumen cannula, were used in a 4X4 Latin-square design, by allocating them to one of four diets with different hay to concentrate ratio and concentrate type. The diets consisted of 0.5 kg hay and 0.75 kg either starchy (HRSC) or fibrous (HRFC) concentrates, or 0.25 kg hay and 1.0 kg either starchy (LRSC) or fibrous (LRFC) concentrates. The diets were designed to provide similar intakes of energy and crude protein. Volatile fatty acids (VFA) and ammonia concentrations, pH values and number of protozoa were determined in wether rumen fluid. Total VFA concentration was not significantly affected by diet but acetate and n-butyrate proportions were higher (P<0.001) on the higher forage diets and propionate higher (P<0.001) on the lower forage diets. pH values and number of protozoa in sheep rumen fluid were unaffected by treatment, while ammonia concentration was lower (P<0.05) on the HRFC diet. In the second trial, 60 lactating dairy ewes were allocated to one of four diets for weeks 11 to 15 of lactation (period 1). Ewes were given food daily: 0.87 kg hay and 1.3 kg either HRFC or HRSC concentrates, or 0.4 kg hay and 1.6 kg either LRFC or LRSC concentrates. During weeks 16 to 20 of lactation (period 2), the ewes were given the same amount and type of concentrates but hay was supplied ad libitum and this period formed the third trial. Milk yield and milk composition were affected significantly by hay to concentrate ratio with the lower hay to concentrate ratio resulting in a significant increase in milk yield, milk protein efficiency, protein content and protein and lactose yields. Milk fat content and yield were reduced. Hay intake was proportionately greater (P<0.001) by 0.15 to 0.20 with starchy than with fibrous concentrate diets in period 2. Problems such as acidosis or 'off-food' periods in ewes given the low hay to concentrate ratio diets were not observed, irrespective of concentrate type.