Responses in Feed Intake, Digestibility and Nitrogen Retention in Lactating Dairy Goats Fed Increasing Amounts of Urea and Fish Meal

Hay intake, milk production and rumen fermentation in British Saanen goats given concentrates varying widely in protein concentration

About 8 weeks after parturition six multiparous British Saanen goats with permanent rumen fistulas were allocated to three dietary treatments in a random sequence for three successive 30-day periods. The treatments were perennial ryegrass hayad libitumwith 1000 glday of concentrates containing 112 (low-protein, LP), 182 (high-protein, HP) or 255 (very high protein, VHP) g crude protein (CP) per kg dry matter (DM) daily. The CP concentration was increased by substitution of soya-bean meal for cereals. From day 19 of each period, when measurements were made, concentrate allowance was reduced to 850 glday and hay intake was offered at proportionately 0·10 more than consumption in the previous 6 days. Hay intake and milk yield increased linearly with CP in the concentrates, but differences between HP and VHP were small and non-significant. Milk composition was unaffected by the treatments, so yields of milk solids followed the same trends as yields of milk, but these were only significant for solids-not-fat. The digestibility of neutral-detergent fibre, acid-detergent fibre and nitrogen (N) all increased with increasing CP, but significantly so only for N; the digestibility of DM and organic matter was unaffected.

The digestibility of the hay incubated in the rumen was unaffected by the treatments. With increasing N intake, faecal, urine and milk N increased linearly as did apparently digested N but N retention did not follow a consistent pattern. Rumen volatile fatty acids and pH were unaffected but concentration of rumen ammonia and blood urea increased with increasing CP as did rumen fluid dilution rate. The results suggest that, with lactating goats given diets of moderate quality grass hay and concentrates containing soya-bean meal, responses to concentrations of CP greater than about 180 g/kg DM in the concentrates or 140 g CP per kg DM in the total diet are likely to be small.

The effect of amount of protein in the concentrates on hay intake and rate of passage, diet digestibility and milk production in British Saanen goats

During the first 2 weeks after kidding, 27 multiparous British Saanen goats were offered 1·5 kg hay (98 g crude protein (CP) per kg dry matter (DM)) and from 0·45 increasing to 0·70 kg concentrates (152 g CP per kg DM) daily. Week 2 was used as a covariance period. At week 3 of lactation all the goats were allocated to one of three groups and were offered hay ad libitum and 1 kg concentrates containing 117 (LP), 152 (MP) or 185 (HP) g CP per kg DM daily to week 15. During weeks 4 to 15, hay intake and milk yield were highest in the HP group. With increasing protein in the concentrates, hay DM intake was 1·20, 1·19 and 1·37 (s.e. 0·060) kg/day respectively and milk yield was 3·04, 3·21 and 3·36 (s.e. 0·080) kg/day respectively (linear response P < 001). There was no significant effect on the concentration of solids-not-fat, fat, total nitrogen or casein in milk. The digestibility of dietary organic matter, acid-detergent fibre and total nitrogen measured after week 15 was significantly greater with HP than with LP (P < 0·05), with MP values being intermediate (linear response P < 005). The rate of passage of ytterbium-labelled hay was unaffected by the treatments. The results indicate that, with lactating goats given hay and concentrates, beneficial responses may be expected to increasing concentrate CP to at least 185 g CP per kg DM.

Methods to study degradation of ruminant feeds

Ruman degradation is crucial in the supply of dietary nutrients to meet the nutrient demands of the anaerobic microbes and body tissues of ruminant animals. Therefore, it is essential to study the dynamics of rumen degradation of various feeds before their potential use to formulate nutritious diets for ruminant animals. Amongst many methods that have been used in the past, thein saccomethod has been the most effective method to study rumen degradation. However, this method is undesirable due to its implications for animal welfare and costs. While manyin vitromethods have been tested as possible alternatives to thein saccomethod to study rumen degradation of feeds, they were unable to remove the need to use fistulated animals to obtain rumen fluid. Although solubility, enzyme- and faeces-basedin vitromethods do not require rumen fluid, they still need data from either thein saccomethod or the rumen fluid-basedin vitromethods for comparison and validation. Therefore, there is a need to developin vitromethods that do not require the need to surgically modify ruminants to obtain rumen fluid to study rumen degradation. We review the potentials and problems associated with the existing methods to study rumen degradation and their implications for the animal industry in different situations.