1. The results are reported of a series of 8-day magnesium metabolism trials carried out with milking cows fed a variety of typical winter stall rations.2. Twelve cows fed a standard ration of 15 lb. hay plus 12 lb. of a concentrate mixture containing 3 parts dredge corn, 1 part bran, 1 part decorticated groundnut meal and 1 lb./cwt. Churn 105 minerals, showed variations in the proportion of the feed magnesium excreted in the faeces of from 66·53 to 76·98%, probably reflecting individual differences in the capacity of animals to absorb magnesium.3. Wide differences in the utilization of the magnesium in typical winter rations were observed. Mean values, with a standard error, obtained for the proportion of the feed magnesium excreted in the faeces with various types of ration were as follows: hay plus concentrates, 71·48 ± 0·94; hay plus proprietary dairy cubes, 62·15 ± 2·73%; hay, proprietary dairy cubes plus decorticated groundnut meal, 91·98 ± 1·93%; hay, silage (1) plus concentrates, 79·53 ± 0·99%; hay, silage (2) plus concentrates, 74·07 ± 4·24%; hay, mangolds plus concentrates, 74·28 ± 5·91%.

The effect of the level of pre-partum feeding of Friesian heifers on the yields and composition of the milk in the subsequent lactation has been investigated using 23 heifers on each of 2 treatments. For 1 treatment, over a period of 6 weeks before calving, generous grazing on good pasture was supplemented with 8 lb/ cow daily of concentrates, and for the other only restricted grazing of an already sparse sward was allowed.For the period 3-8 weeks from calving the heifers fed at the high plane pre-partum produced significantly more milk than those fed at the low plane (36-8 compared with 31-9 lb/cow daily). The solids-not-fat (S.N.F.) and fat contents of their milk were also significantly higher (8-71 compared with 8-47 %, and 3-72 compared with 3-38 %, respectively). For the period 3-14 weeks from calving the effect of milk yield was slightly greater but the effect on composition was less. For the period 3-30 weeks from calving the difference in milk yield remained significant (31-3 compared with 26-1 lb/cow daily), but the average differences in S.N.F. and fat contents over this period (8-63 compared with 8-51%, and 3-75 compared with 3-59%, respectively) were not significant.The heifers fed at the higher plane increased in liveweight before calving at a rate which was highly significantly greater than that of the heifers fed at the low plane. After calving, the heifers which had been on the higher plane remained almost constant in weight during the first 12 weeks whilst the others regained some of their losses, a difference which was highly significant. This recovery was apparently made at the expense of milk yield and composition.The effect of the level of feeding of the cow before calving on the subsequent yield and composition of milk was reviewed by Burt (1956) and Broster (1958). Since then Castle & Watson (1961) have compared the feeding of 3-3 and 1-6 cwt of concentrates during the last 5 weeks before calving, as an addition to good pasture, and found no response in milk yield. On the other hand Swanson & Hinton (1962), using 75 pairs of cows, found that the addition of 8 lb of concentrates per cow daily to a roughage ration during the last 6 weeks before calving gave an increase of 302 lb of fat-corrected milk in the first 15 weeks of lactation. There was no evidence of an effect on milk composition in either of these investigations, but in other investigations the level of feeding before calving has been shown to influence milk composition particularly in early lactation, and the following summary is confined to these papers.

The effects, on the yield and composition of the milk of the cow, of additions to the diet of the calcium salts of acetic, propionic, butyric or lactic acids were determined in 3 change-over experiments. In all cases yield of milk was increased slightly and milk fat content was reduced; solids-not-fat (SNF) percentage was depressed by acetate and butyrate. The effects of these treatments differed markedly from those observed previously when dilute solutions of the corresponding acids were infused into the rumen, but the relative effects of the calcium salts were similar to those of the free acids. It was concluded that the specific effects of the acids were overshadowed by a more marked general effect arising from their addition to the diet as calcium salts. This was confirmed in a subsequent experiment with fistulated cows, in which the effect of an infusion of propionic acid into the rumen was compared with that of an infusion of calcium propionate and of calcium propionate given with the diet. The effect of the addition to the diet of calcium in the form of carbonate differed from that of calcium salts of the fatty acids. It was concluded that the salts were not likely to find practical use.In the lactating cow, continuous addition to the rumen of dilute solutions of the short chain fatty acids or of lactic acid, causes changes in milk yield and composition: acetic acid increases milk yield and fat content, but has no effect on the content of milk SNF; propionic acid decreases milk fat and increases SNF; butyric acid increases milk fat, and lactic acid decreases milk fat and increases SNF though to a lesser extent than does propionic acid (Rook & Balch, 1961). The composition of the basal diet affects the extent, but does not change the nature, of the responses to additions of acetic or propionic acid (Rook, Balch & Johnson, 1965).Under practical farming conditions, solutions of acids cannot be administered to cows in amounts sufficient to influence milk yield and composition. A possible alternative is to add to the diet salts of the acids. Sutton (1964) reviewed the more important experiments in which the effects on milk composition of additions of sodium acetate to the diet of milking cows have been examined, and concluded that the daily addition of up to 450 g of sodium acetate (equivalent to 200 g of acetic acid) * Present address: Department of Agriculture, The University, Leeds 2. 13 Dairy Res. 34 200 C. C. B A L C H AND OTHERSto diets low in roughage usually, but not invariably, raised milk fat percentage. A similar conclusion was reached by Balch & Rowland (1959) after experiments in which they infused up to 1-5 kg of sodium acetate into the rumen of cows. More recently, Jorgensen, Schultz & Barr (1965) found that milk fat content, depressed by a diet high in maize and low in roughage, was not restored by a dietary addition of sodium acetate. The addition of larger quantities of the sodium salts to provide amounts of acids equivalent to those infused in the experiments of Rook & Balch (1961) causes ha...

The changes in chemical composition during haymaking, the loss of nutrients in the field and during storage, and the nutritive value of swath-cured and tripoded hay were compared. In good weather no advantage was gained by tripoding the hay. The nutritive value of the hays made by the two methods was similar and the loss of dry matter in the field slightly lower in the swath-cured hay. In a bad season, however, the nutrient loss in the swath-cured hay greatly exceeded that occurring in the tripoded hay and the starch equivalent, as shown by the results of digestibility trials, was markedly lower for the swath-cured.

In the results from a previously reported uniformity trial on pasture evaluation, there appeared to be systematic areal changes in the crude fibre and crude protein percentages of the herbage. These trends have been illustrated by the calculation of quadratic contours and the possible relationships of the changes to local soil differences, moisture percentages and copse shelter effects have been investigated.