An investigation into growth in Jersey, Holstein and Hereford heifers on kikuyu pasture (Pennisetum clandestinum) using N-Alkanes to estimate intake and ruminal outflow rate.

Abstract

The experiment was designed to investigate why dairy heifers perform poorly on kikuyu pasture compared to a beef breed like the Hereford. The main assumption was that the lower growth rate in dairy breeds was due to low intake as a result of slower passage of digesta out of the reticulorumen. Eight animals in each breed (Jersey, Hereford and Holstein) were grazed continuously on 6.25 hectares of kikuyu. The Jerseys had to be dropped from the second part of the experiment due to health problems. The experiment was conducted from December to April and was split into two trials with half the animals in each breed on a maize supplement during the last eight weeks of the experiment. During the first trial (T1), average daily gain was 1.18, 0.54 and 0.2 kg per daily in Herefords, Holsteins and Jerseys respectively. Herefords grew significantly faster than both the Holsteins and the Jerseys (p<0.01). The Holsteins also grew significantly faster than the Jerseys (p<0.05). In trial 2 (T2), average daily gains were 0.732 and 0.561 in Herefords and Holsteins respectively. Supplemented Herefords had and average daily gain of 0.797 compared to 0.668 kg in non-supplemented animals. Supplemented Holsteins had an average daily gain of 0.497 compared to the 0.624 in non-supplemented animals. There were no differences in growth in T2 (p>0.05). N-alkane estimated intake in T1 using the C32/C33 alkane pair was 117.7, 92.7 and 97.6g/kg LW(0.75) in Herefords, Holsteins and Jerseys respectively. The Herefords had significantly higher intake compared to both the Holsteins and the Jerseys (p<0.05). In T2, the Herefords had a significantly higher intake (p<0.05) of 104.4 compared to 98.0g/kg LW(0.75) in the Holsteins. In T1, n-alkane estimated digestibility was 59.8, 56.8 and 51.4% in Herefords, Holsteins and Jerseys respectively. The Herefords had significantly higher apparent digestibility compared to the Jerseys (p<0.05). In T2, the Herefords had a digestibility of 61.6 compared to the Holsteins at 60.5%. The difference was not significant (p>0.05). Estimated outflow rate (kl) using Cr(2)O(3) was 0.056, 0.062, 0.061 and 0.056/h in supplemented Herefords, non-supplemented Herefords, supplemented Holsteins and non-supplemented Holsteins respectively when data was fitted into a multi-compartment model. When the data was fitted into a two-compartment model, estimated kl values were 0.069, 0.063, 0.090, and 0.061/h also respectively. When data obtained from using alkane coated hay was used, kl values obtained by a graphical procedure were 0.035, 0.042, 0.038 and 0.042/h also respectively. Neither breed nor supplement had a significant effect on outflow rate (p>0.05).