Low-yielding Cows Research Articles

Endocrine control of energy metabolism in the cow: comparison of the levels of hormones (prolactin, growth hormone, insulin and thyroxine) and metabolites in the plasma of high- and low-yielding cattle at various stages of lactation.

To obtain information on the physiological mechanisms controlling the partition of dietary energy between body weight and milk production in lactating cattle, the concentrations of hormones (prolactin, growth hormone, insulin and thyroxine) and metabolites (glucose, non-esterified fatty acids, β-hydroxybutyric acid and l-lactic acid) in plasma obtained from eight high-yielding and seven low-yielding cows, matched for diet and stage of lactation, were compared. Blood samples were taken via a jugular catheter, throughout four 48 h periods at various times during lactation (days 40, 80, 120 and 180) and also when the animals were dry. The milk yield rose for 7 weeks after parturition, reaching peak values of 24·8 and 10·1 kg/day in the high- and low-yielding groups respectively. The body weights of the low-yielding animals rose steadily, whereas cows in the high-yielding group lost weight up to week 14 of lactation and thereafter gradually gained weight. No differences were found between the groups in the digestibility of the diets, although analysis of the rumen fluid indicated small differences in the proportions of volatile fatty acids. Milk analysis suggested that the protein content of milk obtained from low-yielding cows was greater than that of milk from high-yielding animals. Throughout lactation, the concentrations of growth hormone (P < 0·001), non-esterified fatty acids (P < 0·01) and β-hydroxybutyric acid (P < 0·05) were higher in the high-yielding than in the low-yielding group, whereas the concentration of insulin was higher (P < 0·01) in the low-yielding animals. The level of thyroxine was higher (P < 0·05) in the low-yielding group when the animals were dry. A comparison of peak lactation (days 40 and 80) with the dry period demonstrated that the concentration of prolactin was higher in both groups high-yielding, P < 0·01; low-yielding, P < 0·001) when the animals were dry and the concentration of thyroxine in the low-yielding cows was higher (P < 0·01) when the animals were dry. Significant reductions in the concentrations of growth hormone (P < 0·001) and non-esterified fatty acids (P < 0·001) were accompanied by an increase in the concentration of glucose (P < 0·01) when the high-yielding animals were dry.

Physiological factors affecting the voluntary intake of feed by cows: A review

Physiological factors affecting voluntary dry matter intake (VDMI) by cows were studied. An excess energy intake is often observed when low-yielding cows are consuming high energy diets. This does not suggest a regulation of intake such as to maintain energy balance. Variations of VDMI between animals and during lactation were analysed. Evidence was obtained for a good enough adjustment of intake to the cows' needs when highly “ingestible” and high energy diets are given, but a failure of this regulation is observed at the beginning and at the end of lactation. Some aspects of metabolic and hormonal control and of physical limitation of intake were reviewed and some practical consequences of the studies on voluntary dry matter intake regulation were drawn.

Effort and time in pipeline milking.

Effort and time spent in machine milking using pipeline vs. bucket milking methods were compared in a conventional cowshed and in a 2-level milking parlour. In each case 2 units were used and cows were machine-stripped. In the cowshed data were obtained for each of 6 milkers milking 20 low-yielding cows; in the parlour each of 3 milkers milked 21 moderate yielding cows. Total energy expenditure (measured at one milking only for each of the cowshed milkers) averaged 5.0 kcal./min., but considerable variation was shown between workers. In the cowshed mean heart rate was similar for the 2 milking methods but in the parlour heart rates were higher for bucket than pipeline milking; the former also involved greater increase in effort in carrying the filled cans and in cleaning the milking equipment. Milking time for the bucket method exceeded that for the pipeline method by 18% and 9% in cowshed and parlour respectively. Practical aspects are discussed. R.B.S. (Abstract retrieved from CAB Abstracts by CABI’s permission)

The feed intake of grazing cattle III. The influence of level of milk yield

SUMMARY1. The feed intakes of 18 Ayrshire cows continuously grazing a timothy-meadow fescue-white clover sward were estimated by the chromic oxide-faecal nitrogen method for two 6-weekly periods, one in 1960 and one in 1961. The cows consisted of (1) 6 lactating cows, 6–7 months post partum (Low yield), (2) 6 lactating cows, 2 months post partum (High yield) and (3) 6 dry cows; their live-weights, milk yields and milk composition were recorded.2. The mean organic matter digestibility of the herbage consumed in the two experiments was 78·2 and 76·2%. The mean digestible organic matter intakes (DOMI) were 23·3, 24·7 and 17·6 Ib./day for low yield, high yield and dry cows respectively.3. The mean daily fat-corrected milk (FCM) yields of the low and high yield cows were 29·1 and 34·3 lb. in the first experiment, and 26·8 and 42·8 lb. in the second. The mean live-weights of the lactating groups were 1036 lb. and 1106 lb. in the two experiments and did not differ between yield levels.4. DOMI was partitioned between maintenance, live-weight gain and FCM yield by regression analysis. Significant partial regression coefficients of DOMI on FCM varying between 0·221 and 0·272 were obtained. It was concluded that milk production accounted for about 0·24 lb. DOMI per lb. FCM.5. The results are discussed with particular regard to other estimates of the effect of milk production on the DOMI of the grazing cow and to the estimation of the maintenance requirement for DOM by the grazing animal.