The effects of the presence or absence of vasectomized male buffaloes on the reproductive
efficiency of buffalo cows (n = 396) undergoing artificial insemination (AI) was studied on six
farms owned and operated by a single consortium. Lactating animals were separated into two
groups of various sizes on each farm and kept under semi-range conditions. Vasectomized bulls
were present in one group at a bull/empty-cow ratio of 1:30. No bulls were present in the other
group. Reproductive efficiency between the two groups over a period of 3.5 months was compared
and evaluated on the basis of: 1) the number of spontaneous overt estruses associated with either
feeble or intense signs of estrous behaviour; 2) the number of functional estrous cycles, i.e. estrous
cycles with luteal phases defined as normal, based on specified progesterone concentrations in
milk or blood plasma 8-10 days after estrus; 3) the number of consecutive functional estrous
cycles in cases of induced estrus; and 41 pregnancy rate.
Groups with bulls present demonstrated a significantly higher reproductive efficiency than
groups without them. There was a higher incidence of spontaneous estrus (92 versus 69%;
P < 0.01); spontaneous estrus of high intensity (62.2 versus 31.1%; P < 0.01); and higher
incidence of functional estrous cycles following both spontaneous (65.8 versus 57.1%) and
induced (77.0 versus 59.5%; P < 0.05) es&us. Exposure to vasectomised bulls also increased the
incidence of consecutive functional estrous cycles (90.5 versus 68.1%; P < O.Ol>, and the
pregnancy rate in cows inseminated at spontaneous (42.5 versus 18.9%; P < 0.01) or induced
(5 1.1 versus 33.3%; P < 0.05) estrus. Overall pregnancy rate did not differ significantly between