Abstract
The objective of this study was to investigate the effects of either maize or sulla silage supplementation to grazing dairy cows in summer. Forage mixtures used in the four week trial were based on previous experimental results but inclusion of rumen fistulated cows in five treatments enabled rumen sampling and use of in sacco incubations to determine the diet effects on digestion kinetics. Sulla and maize silages were used to supplement pasture and to meet minimum requirements for dietary protein concentration. Five groups often cows were grazed on a restricted daily allowance of 18 kg dry matter (DM) pasture/cow to simulate a summer pasture deficit, and four of these five groups received an additional 6 kg DM cow -1 d -1 of silage (sulla, maize, or sulla and maize silages). A sixth group was given a relatively unrestricted (38 kg DM cow -1 d -1 ) pasture allowance. The silage mixtures and pasture were incubated in sacco during the final week of the trial. The pasture was of high nutritive value and not typical of usual summer conditions, which favoured a response to quantity rather than quality of silage supplements. There was no difference in cow performance with the four silage supplements and the low milk solids (MS) production (about 1.0 kg MS d -1 ) relative to full pasture (1.3 kg MS d -1 ) showed the principal limitation to performance was dry matter intake. Milk composition was not affected by silage type and the low level of pasture substitution (0.29) suggested metabolizable energy (ME) was the principal limitation to performance. Samples of rumen liquor and in sacco data demonstrated significant effects of supplement; DM degradation rates (k) was highest (0.084 h-') when cows were fed 6 kg sulla silage whereas diets with a high proportion of maize silage were slowly degraded (p<0.01).
Highlights
A previous study examined responses to maize, pasture, lotus (Lotus corniculatus L.) and sulla (Hedysarum coronarium L.) silage supplementation and showed clear benefits of lotus silage for milk production when pasture supply was restricted (Woodward et al, 2002)
The main effect of silage supplementation was through provision of additional metabolizable energy (ME) the non-structural carbohydrates (NSC) content of maize silage did alter diet composition
The fibre effective degradability for pasture and pasture supplemented with 6 kg dry matter (DM) sulla silage cow-1 d-1 were about 30% higher than other supplemented cows treatments (Table 3)
Summary
A previous study examined responses to maize, pasture, lotus (Lotus corniculatus L.) and sulla (Hedysarum coronarium L.) silage supplementation and showed clear benefits of lotus silage for milk production when pasture supply was restricted (Woodward et al, 2002). Maize silage did maintain milk production over the four week experimental period the cows did not gain weight in contrast to other silages and the dietary CP was less than cow requirements (NRC, 2001). The poor cow response to maize silage, in contrast to lotus silage (14.97 vs 17.23 kg milk, respectively; Woodward et al, 2002) emphasised the importance of meeting cow protein requirements especially as maize silage has a very low protein concentration (6.9% DM) and is not suitable for feeding with low quality summer pasture. Balancing dietary protein deficiency by feeding sulla and improving readily fermentable carbohydrate intake with maize silage may optimise milksolid production from cows grazing poor to medium quality in summer in Chaves et al, (2006) Asian-Aust.
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