566. Studies of the secretion of milk of low fat content by cows on diets low in hay and high in concentrates: V. The importance of the type of starch in the concentrates

Abstract

1. Three comparable groups of cows were used to investigate the effect, on milk composition and yield, of diets consisting of 4 lb. hay daily and concentrates containing 35% weatings, 15% decorticated groundnut cake and 50% of either flaked maize, maize meal or dredge corn (crushed oats and barley) respectively.2. During initial and final control periods all the cows received 16 lb. hay daily and, per 10 lb. of milk produced, they received about 4 lb. of the concentrate mixture containing flaked maize. During the experimental period of 6 weeks all the cows received 4 lb. hay, concentrates according to milk yield, and an extra 7 lb. of concentrates daily. One group of cows received the concentrate mixture containing flaked maize, a second group the mixture with maize meal and the third group that with dredge corn. The mean daily intakes of starch for the different groups were respectively 6·0, 6·4 and 5·8 lb. per cow.3. The diet containing flaked maize caused a marked, and that containing maize meal a small fall in the fat content of the milk, but the diet containing dredge corn was without effect. In the last 2 weeks of experimental treatment the adjusted mean fat percentage for the group of cows receiving flaked maize was 0·51 and 0·71 below the percentages for the groups receiving maize meal and dredge corn respectively. The yields of milk and of milk fat were also lower in the group receiving flaked maize than in either of the other groups, but the experimental treatments produced no changes in the milk solids-not-fat percentage.4. This experiment has shown that when diets low in hay and high in concentrates are given to lactating cows, the type of starch in the concentrates is of great importance in determining the extent of the depression in milk fat percentage. The greater depression with flaked maize than with maize meal or dredge corn is thought to be associated with the effect of the starch on the flora of the reticulo-rumen.

Effects of high-grain diets and 1,3-butanediol on production of milk fat and protein in cows

“…Contrary to expectation and previous results reported in the litera ture (Balch, 1955;Storry and Rook, 1966), fat depression was not very marked on the fat depressing diet. As a result, the response to feeding BD was not very conclusive.…”

“…Other dietary ingredients which cause similar results are pelleted roughage (King and Hemken, 1962), pelleted or heat treated corn Balch, 1955), finely ground hay (Colenbrander al., 1968;Emery ejt al., 1964a), and cod liver oil .…”

“…A well known cause of fat depression is lush spring grass which is very low in fiber, but supplementation of pasture with corn silage will alleviate this condition (Huber et al, 1964). Balch (1955) found in stud ies with flaked corn as the concentrate that the more fibrous the roughage source, the less fat was depressed. It would seem that more fiber in the diet would slow down passage and allow more time for fermentation and absorption of milk fat precursors.…”

Milk composition in relation to rumen metabolism

“…These observations conform with those of Phillipson (1952) on lambs fed on rations rich in flaked maize. Rations containing normal quantities of roughage offered in ground form produce similar changes in the products of rumen fermentation (Balch & Rowland, 1957).…”

“…On dry feeds, the depression in milk-fat secretion is independent of the type and level of protein in the ration (Balch, Balch, Bartlett, Cox, Rowland & Turner, 1954) but is particularly marked on rations rich in readily soluble carbohydrates, e.g. those containing large amounts of flaked maize (Balch, Balch, Bartlett, Hosking, Johnson, Rowland & Turner, 1955).…”