Effect of bull biostimulation on the oestrous behaviour of pubertal Sahiwal (Bos indicus) heifers

The study was conducted to determine effects of biostimulation of Sahiwal heifers through fenceline bull contact and fenceline combined with direct bull contact on oestrous behaviour when there was ovulation occurring in the absence of behavioural oestrus ("silent oestrus - SE) and overt behavioural oestrus (OBE). Prepubertal Sahiwal heifers were allotted to three treatments (T-0, T-1, T-2, n = 8 heifers/treatment). In the T-0 group, there was no bull exposure; in T-1, exposure to a bull through fenceline contact for 24 h and in T-2, exposure to a bull as in T-1 along with direct bull contact with another bull for a 6 -h period daily. The oestrous behaviours were recorded on day (d) -3, -2 and -1 (prior to oestrus), d 0 (day of oestrus) and d +3, +2 and +1 (post-estrus). With both SE and OBE, the mean frequency of sniffing, micturition, chin resting and standing to be mounted differed (P < 0.05) from d -2 to d +1 among treatment groups. The mean times devoted to eating, ruminating and lying during SE and OBE were less (P < 0.05) on d-1 and d 0 in heifers of all three groups than the respective values on reference days in both T-1 and T-2 groups. Biostimulation of Sahiwal heifers with bull exposure, therefore, resulted in greater expression of oestrous behaviour than in non-exposed heifers during the periods around when there was SE and OBE.