ALBERT

Description: Two studies were conducted at Massey University in 1998. Expt 1 investigated the combined use of n-alkanes and 13C techniques for the estimation of individual proportions and total intakes of herbage (H) and maize silage (MS) by dairy cows. Expt 2 measured the variation in the amount of MS consumed by individual cows fed as a group. In Expt 1, six dry Holstein–Friesian cows were kept indoors and fed a diet containing one of the following H[ratio ]MS ratios (dry matter basis)[ratio ]100[ratio ]0, 80[ratio ]20, 60[ratio ]40, 40[ratio ]60, 20[ratio ]80 or 10[ratio ]90 for 25 days. Cows were dosed with a slow-release capsule containing 8 g of dotriacontane (C32) and 8 g of hexatriacontane (C36). Intake estimates were based on individual faecal samples collected twice daily during two 5-day periods. In Expt 2 (grazing trial), 12 early-lactation cows were selected from a commercial herd of 48 autumn-calving cows and blocked into pairs according to milk yield, lactation length and lactation number in a complete block randomized design. Within each pair, cows were randomly assigned to two treatments: supplemented, S (4 kg MS DM per cow after the morning milking in feed troughs) or not supplemented, NS. Another eight cows were randomly selected from the rest of the herd to increase the number of individual estimations of H and MS intakes. Cows grazed perennial ryegrass-white clover pasture during the rest of the day. In Expt 1, H[ratio ]MS ratios were not accurately predicted by the odd-chained n-alkanes, but there was a strong linear relationship between the concentration of 13C in faeces and actual H: MS ratios in the diet. The 13C method was therefore combined with the n-alkanes, resulting in accurate estimations of H and MS intakes. In Expt 2, a large variation was observed among individual cows in their daily intakes of MS (range 0·94 to 5·09 kg DM per cow, coefficient of variation = 36%), but this variation in MS intake was not associated with milk yield (P 〉 0·05). The results indicate that the n-alkane and 13C techniques can be successfully combined to estimate the intake of MS and H of grazing cows supplemented as a group. Under the conditions of the present study, individual cows differ considerably in the amount of maize silage consumed per day, although the reasons for this are not clear.

Description: A statistical model of the grazing preference of sheep is presented for the evaluation of spaced plants in small plots for plant breeding purposes. Plants are located randomly to reduce the effect of external factors on diet selection, and to differentiate between discriminatory and random grazing. Consistency of discrimination among grazings and sites (Massey University, New Zealand and INIA La Estanzuela, Uruguay) was tested. The statistical design and subsequent analyses considered all sources of variation to minimize error, and to separate genetic effects from environment effects. Clonal replicates were used to enhance error-control, and hence the precision of heritability estimates, as most characters are inherited quantitatively. Post-grazing leafiness is considered the best character to select and breed for animal preference in a red clover germplasm.

Description: A spaced plant experiment and a sward experiment were conducted at INIA La Estanzuela, Uruguay in 1996 with six red clover (Trifolium pratense L.) populations, to study the efficacy of selecting genotypes for sward performance in a spaced plant nursery. This was examined through: (a) the ranking of the best linear unbiased predictors (BLUP) of populations and (b) the ratio of the correlated genetic advance in swards by selecting under spaced plant conditions to the direct genetic advance of selecting under sward conditions. From the eight characters analysed, only the rankings of BLUPs for leaf size and flowering were significantly the same between populations. The other six characters performed differently according to the level of competition imposed. Post-grazing leafiness and the difference between pre- and post-grazing leafiness (the two most important characters to measure preferential grazing) achieved greater genetic advance when selection was done as spaced plants: while for pre- and post-grazing height genetic advance was greatest by selecting under sward conditions. For other characters, the best conditions to select depended on the selection intensity achievable.