Ninety-six Friesian cows were used to determine the effects of pattern of allocation of a fixed amount of concentrates on milk yield during the treatment and residual periods (weeks 1–20 and 21–44 respectively) and on the whole lactation. Thirty-two were in their second and the remainder in their third or later lactation. Second-lactation cows were used to form separate blocks.
Four treatments were imposed for the first 20 weeks of lactation; these were Graded (G), Woodman (W), High Fixed (HF), and Low Fixed (LF). The first three treatments involved the same total amount of concentrate but fed in different daily amounts. Treatment W received Woodman's standard (Evans, 1960) amounts of feed according to a predetermined lactation curve derived from earlier experience in the herd; treatment G reallocated the same allowance by feeding more than W in weeks 1–12 and less during weeks 13–20; the HF treatment was a fixed daily amount of 6·4 kg, in total also equal to W total. LF was a fixed daily amount of 4·0 kg/day. The maintenance allowance was the same for all cows within a block and based on hay, dried sugar-beet pulp and barley meal. During weeks 21–44 all cows within a block received the same treatment; either grazing or self-fed silage and supplementary concentrates according to the time of year.
There were significant differences in milk yield during the treatment period resulting from plane of feeding (W, G and HF greater than LF; P < 0·001) but no significant differences arising from the pattern of feeding. In the residual period (weeks 21–44) there was no significant difference between the yields of second-lactation treatment groups. Thus for the whole lactation the yields of treatments G, W and HF were significantly greater than LF. However, for the older cows there were differences in the residual period and treatment groups G and LF gave significantly more milk than group W (P < 0·001 and P < 0·05 respectively). Over the whole lactation treatment group G gave significantly more milk than LF (P < 0·001), W (P < 0·01) and HF (P < 0·05). Furthermore, the increase in total lactation yield of G compared with W was 4·5 times the increase observed in weeks 1–20.
Cows of both age groups on treatment HF, unlike those on treatments W and G, never achieved a distinct peak yield but their mean weekly rate of decline was significantly less.
Live-weight changes varied between treatments and between age groups and were significantly correlated with milk yield in weeks 1–20.
There were no significant effects of treatments on milk composition in either age group at any stage of the lactation. The minimum value for solids-not-fat content for the cows on the LF treatment was unacceptably low.
It is suggested that for cows of moderate yield potential fed to Woodman's standards (Evans, 1960) the actual pattern of feeding a predetermined amount of concentrates has little effect on the yield or quality of milk. For cows of high potential a redistribution of concentrates to allow earlier more generous feeding will increase milk yield.
The rate of decline of milk yield is a characteristic of both cow potential and pattern of feeding and an adoption of a standard 2½% a week should be viewed with caution.