Nutrient supply and growth of cattle offered straw-based diets.

An experiment was conducted using steers cannulated at the rumen, duodenum and ileum to study the effects of increasing the levels of barley and fishmeal in straw-based diets. Diets A, B, C and D contained ammonia-treated straw, barley and fishmeal in the ratios, 67:33:0, 66:23:11, 53:47:0 and 52:36:12 (by weight) and were offered in daily amounts of 3.9, 3.9, 4.8 and 4.8 kg dry matter. The effects of barley were attributable to increased intakes of digestible organic matter and consequently to increased flows of microbial matter to the duodenum. There were no modifications in the balance of energy to nitrogen-yielding nutrients available for absorption. Introducing fishmeal into diets improved digestibility of cellulose and xylose by up to 6.7 and 4.7% respectively, and shifted digestion towards the large intestine. Second, it increased amino acid N supply to the small intestine which averaged 52.2, 63.2, 68.8 and 84.0 g/d with diets A, B, C and D. Some changes were also noted in the balance of amino acids absorbed. Consequently, the contribution of amino acids to metabolizable energy intake increased with the proportion of fishmeal in diets (0.17, 0.20, 0.18 and 0.21 for diets A, B, C and D). Growth rates measured in heifers amounted to 259, 431, 522 and 615 g/d for diets A, B, C and D. They appeared to be related to intestinal amino acid supply.

Effect of amount and composition of feed given over three lactations on the performance of the dairy cow.

Eighty-nine autumn-calving first calf and adult Friesian cows participated in an experiment on the effect of feeding over three lactations on milk production and live weight change. Fixed daily allowances of digestible energy (DE) formed two of the treatments (h, H; moderate, M). Diets of similar composition were used for both treatments and rations were weighed daily for each cow. The cows within these treatments were re-randomized to H or M at second and again at third parturition on experiment. A further treatment (ALF), applied continuously over three lactations, consisted of the M allowance of compound feed, weighed daily for each cow, plus as lib. weighed, group-fed forages. The ALF animals were randomized for each lactation into two groups both of which received the same total compound feed allowance over the first 26 weeks of lactation. For one group (Flat) equal amounts were given daily whilst for the other group (Step) the daily amount was decreased monthly. After week 26 equal rations were fed. Hay, maize silage and grass silage formed the forages in winter. Grass, cut for the H and M groups but grazed for the ALF group, provided the summer forage. Energy intakes covered some 80-110% of requirements. Yields of milk and of milk solids responded similarly for both parties. In the first experimental lactation, treatment H led to greater yields compared with M. H also led to smaller losses of live weight in early lactation, equal gains in mid lactation, and smaller gains in late lactation and the dry period, compared with M. Extension of H into a second lactation increased the advantage in milk and solids yields observed in the first lactation on experiment. Recovery of body reserves on treatment M continued. Treatment H in a second lactation on experiment after M in the first lactation led to even greater compensatory gains in live weight at the expense of milk production. There was no effect in the third lactation of experiment of treatments applied in the first lactation. Treatments H and M applied factorially over lactations 2 and 3 gave the same pattern of treatment effects as in lactations 1 and 2. Treatment ALF broadly supported the same milk yield and live weight change as treatment H but improved fat, protein and lactose yields. Within treatment ALF, Flat and Step distribution of compound led to equal performance. Multiple lactation effects of ALF equalled those of H. The effects on milk composition of H compared with M treatment were variable. In general an advantage accrued to ALF over M but without long term effects.

Feeding frequency for lactating cows: effects on digestion, milk production and energy utilization.

The results are reported of four feeding experiments in which lactating cows were given fixed rations of hay and high-cereal concentrates at different meal frequencies. In Expt 1 the total ration was given in two and twenty-four meals daily and in Expts 2-4, the concentrates were given in two and five or six meals and the hay was given twice daily. The diets contained 600-900 g concentrate/kg. In all the experiments, more frequent feeding of these low-roughage diets reduced milk fat depression and increased milk fat yield. In each experiment the increase was greater with the diet containing the lower proportion of hay. There was no significant effect on milk yield, the protein or lactose contents of the milk or live-weight gain. Digestibility of dry matter, organic matter and energy was increased in one of the experiments but not in two others in which it was measured. More frequent feeding was calculated to increase the net energy secreted in milk and there was a tendency for it to increase the net energy in live-weight gain with diets containing 600 or 700 g concentrate/kg but to decrease it with diets containing 800 or 900 g concentrate/kg. These results are discussed in relation to theories of energy partition in lactating cows. It is concluded that at fixed feed intakes, the main response to increased meal frequency is likely to be a reduction in milk fat depression and that this will be confined to diets containing not more than about 200 g modified acid-detergent fibre/kg dry matter.

The effect of a low-protein ration on milk yield and plasma metabolites in Friesian heifers during early lactation.

1. Sixteen first-calf Friesian heifers were used in a continous treatment design experiment. For 2 weeks after calving they were given a 750 g concentrate, 250 g hay/kg ration with 169 g crude protein (nitrogen X 6.25; CP)/kg dry matter (DM). They were then divided into two groups of eight and given a high-protein (223 g CP/kg DM) or low-protein (107 g CP/kg DM) ration at the rate of 10.8 kg concentrate + 3.6 kg hay for 8 weeks. 2. Milk yield and composition, live weight and blood composition were monitored throughout. A digestibility trial was carried out with six animals on each treatment. 3. The low protein ration reduced DM, organic matter, energy and fibre digestibility significantly (P less than 0.001) so that intakes of digestible energy were not equal and the low-protein group lost more weight than the high-protein group. 4. Milk yield and the fat content of milk were lower in heifers given the low-protein ration (P less than 0.01). The lactose content of the milk was not affected and protein content only slightly reduced (P less than 0.01) by low-protein feeding. When the heifers were all changed onto an adequate protein (190 g CP/kg DM) ration in mid-lactation, those which had previously been under-fed protein appeared to recover in milk yield to the point they might have been expected to reach is given an adequate-protein ration throughout. 5. Concentrations of urea (P less than 0.001) and albumin (P less than 0.05) were reduced by underfeeding protein, but albumin concentration was affected less by diet than by stage of lactation. Blood concentrations of total protein, glucose, sodium, potassium, calcium, inorganic phosphate, iron, copper, haemoglobin and packed cell volume were unaffected by treatment. Blood magnesium concentration was slightly lower (P less than 0.01) with low-protein feeding.