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 ratio s 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, we re used in a 4 x 4 Latin-square design, by allocating them to one of four d iets with different hay to concentrate ratio and concentrate type. The diet s consisted of 0.5 kg hay and 0.75 kg either starchy (HRSC) or fibrous (HRF C) 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 concentra tions, pH values and number of protozoa were determined in wether rumen flu id. Total VFA concentration was not significantly affected by diet but acetate and n-butyrate proportions were higher (P < 0.001) on the higher forage die ts and propionate higher (P < 0.001) on the lower forage diets. pH values a nd number of protozoa in sheep rumen fluid were unaffected by treatment, wh ile 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 II to 15 of lactation (period I). Ewes were given food dail y: 0.87 kg hay and 1.3 kg either HRFC or HRSC concentrates, or 0.4 kg hay a nd 1.6 kg either LRFC or LRSC concentrates. During weeks 16 to 20 of lactat ion (period 2), the ewes were given the same amount and type of concentrate s but hay was supplied ad libitum and this period formed the third trial. Milk yield and milk composition were affected significantly by hay to conce ntrate ratio with the lower hay to concentrate ratio resulting in a signifi cant increase in milk yield, milk protein efficiency, protein content and p rotein and lactose yields. Milk fat content and yield were reduced. Hay int ake was proportionately greater (P < 0.001) by 0.15 to 0.20 with starchy th an 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 we re nor observed, irrespective of concentrate type.