Four digestibility and balance experiments were carried out in which 33 growing heifers were fed basal diets of low dry matter silage offered ad libitum, supplemented with various levels of barley and/or groundnut meal or urea.Voluntary intake of the silages was low although apparent digestibility of D.M. was high (66-75 %). There was a significant linear negative relationship between the intake of D.M. as supplement and silage D.M. intake.Apparent digestibility of crude fibre in the silages was high (74-83 %). It was depressed significantly by addition of barley but not by addition of groundnut. There was a highly significant linear relationship between the digestibility of D.M. and G.B. in the mixed silage concentrate diets used. Metabolizable energy (M.E.) values for the silages varied from 2-04 to 2-52 Mcal/kg (8-5-10-5 MJ/kg) D.M. Supplementation with barley at approximately 1 % of live weight, increased M.E. values of the mixed diets to 2-57-2-85 Mcal/kg (10-8-11-9 MJ/kg) D.M. Additional N had little effect on these values. Nitrogen retention was significantly increased in all experiments by barley supplementation. It was further significantly increased by groundnut in three experiments and by urea in one experiment.Multiple regression analysis showed that N retention was significantly related to both M.E. intake and intake of absorbed N, and to M.E. intake and intake of supplementary N.Apparent availabilities of Ca and Mg in silage based diets were low and the availability of Na varied with Na intake. Supplementation with either energy or nitrogen increased apparent availability and retention of Mg but did not exert consistent effects on availability or retention of Ca or Na.There was a highly significant linear relationship between ingested and digested Na but not for Ca or Mg. There was a highly significant linear relationship between absorbed and retained Ca and Mg, but not for Na.Animals fed second cut silages had rather low blood glucose levels and higher than normal levels of blood ketones.

Twenty-seven castrate male cattle were used in two nutritional balance and slaughter experiments to measure the effects of increasing levels of dietary protein (9 to 15% in the dry matter) at two levels of feeding (approximately 16 and 22 MJ metabolizable energy (ME)/100 kg live weight (LW) per day) on digestibility, nitrogen (N) balance and carcass growth and composition over the LW range 130 to 390 kg. The higher level of feeding increased LW gain and carcass gain (CG) but higher protein intake increased LW gain and CG only at the higher feeding level as a result of its favourable effect on digestibility. N balance tended to overestimate carcass N retention at higher levels of protein intake. The higher level of feeding increased the separable fat and total fat in the carcass. Increased protein intake had no effect on the lean meat content but increased the percentage protein in the edible portion of the carcass. LW gain, CG and carcass energy deposition were related to ME intake only but N balance and carcass protein gain were related to both ME and digestible crude protein intake.

Twenty-four castrate male cattle were used in two nutritional balance and slaughter experiments to measure the effects of two implantations with 300 mg trenbolone acetate and 36 mg resorcylic acid lactone over the live-weight range 250 to 400 kg. Control and implanted animals were pair-fed barley-based diets of differing protein concentration in the first experiment and the lower protein diet at two levels of feeding in the second experiment.Daily live-weight gain and nitrogen retention were significantly increased by implantation in both experiments. The carcasses of implanted animals contained significantly more lean meat and a higher proportion of meat in the forequarter. The edible portion of these carcasses contained significantly more protein and water and less fat.Live-weight gain and carcass composition were not influenced by dietary protein intake. Increased feeding level improved live-weight gain, suggesting that a higher metabolizable energy intake would give an increased response to implantation.

No abstract

Various forms of magnesium compounds were applied to grassland managed under modern intensive conditions and the effects on yield and composition of the herbage were measured. Magnesium limestone increased hoth yield and magnesium content. Commercial magnesite (MgO) increased the magnesium content rapidly and also gave a small increase in yield. An annual dressing of magnesium sulphate had little effect on magnesium content and tended to depress yield after two years.A marked seasonal effect exists in pasture magnesium content. Increasing the magnesium content had little effect on its distribution within the plant, but it tended to depress calcium and potash.The results are discussed with special reference to recent research on the magnesium metabolism in dairy cattle.