The effect of feeding sweet potato vine-based partial milk substitute on performance of Friesian bull-calves

Abstract

The study was conducted to investigate the potential of a partial milk substitute (PMS) based on sweet potato vines, on performance of Friesian bull calves. Twenty five new-born Friesian calves (mean weight 38.71 ± 4.56 kg) were used in a completely randomized design (CRD) over a seventy day period. Chopped, air-dried sweet potato vine meal was incorporated into a composite marsh at 0, 30, 40, 50 and 60% inclusion with maize bran, fish meal and mineral powder. Milk offered was reduced by one litre after every fortnight with the dietary treatments introduced at 14 days of age together with ad libitum access to drinking water. Proximate and mineral analyses were carried out for all ingredients and dietary treatments. Data on feed intake, rumen degradability, average daily weight gains (ADG) and variable cost per unit of gain were subjected to analysis of variance (ANOVA) using GenStat (7.22, 2008). Means were separated using the Least Significant Difference (p ≤ 0.05; PROC. GLM; SAS, 2001).

Over a period of 70 days, use of the PMS led to a reduction of 120 litters of the amount of milk fed to each calf. Mean daily intake (gd-1) of dry matter was higher (p<0.05) for calves fed PMS (1085) than those fed on milk and pastures (912). The daily crude protein intake for calves fed PMS (216grams) was comparable to the 219.5 gm d-1 among calves fed milk + grazing (M + G) only. Daily energy intake increased from 9.91 MJ (control) to an average 11.52MJ as a result of using PMS. The ADG of calves were higher (p<0.05) for calves fed PMS (mean=300 g d-1), than those fed milk and grazing only (175 gd-1). The Feed: Gain ratio significantly improved, decreasing from 21.67 (control) to an average of 10.2 (PMS). Live weight gain increased from 12.28kg (M+G) to an average of 20.9kg (PMS) over 70 days. Weaning weights (WW) were higher (p<0.05) among calves fed PMS (mean 64.9kg) compared to 53.94kg for the control (M+G). The total variable cost (TVC) of raising the calves increased with increasing levels of SPV inclusion in the PMS but was not significantly different from the TVC of using M+G when SPV was included at 50% and 60%. However, the net variable cost per unit of gain (NVCg) represented by the average variable cost (AVC) was reduced by more than 50% when PMS comprising 30-60% sweet potato vine were used.

The results of this study show that sweet potato vines-based partial milk diets can be used as substitutes to reduce the cost of rearing a calf without adversely affecting its health and yet save more milk for consumption and processing. The results further demonstrate that the Friesian bull-calf can be raised with minimum resource input to add to the financial benefit of livestock farmers.