with one to two calvings. By 60 to 80 days postpartum, the proportion of cows at onset of ovarian activity for cows with three to five calvings was greater than those cows with one to two calvings.
Cows that calved in the dry season completed uterine involution by 24.4 days, which was significantly shorter than the duration of 26.5 days for cows that calved in the rainy season. Cows
with three to five calvings completed uterine involution earlier than those with one to two calvings. It is concluded that bull–cow biostimulation influences reproductive activity in the cow
Ž .
possibly through olfactory cues pheromones . q 2000 Elsevier Science B.V. All rights reserved.
Keywords: Biostimulation; Season; Parity; Postpartum ovarian activity; Zebu cattle
1. Introduction
Reproductive performance is one of the major and most important factors determin- ing the profitability of cattle herds, with the ideal goal to be achieved being one calf per
cow per year. Reduced calving rates and long calving intervals associated with cattle indigenous to tropical Africa have been serious constraints to the cattle industry
Ž .
Oyedipe et al., 1980; Eduvie, 1985 . A calving to conception interval of not more than Ž
80–85 days is required in order to obtain one calf per cow per year Louca and Legates, .
1968 . In some countries, this interval is invariably prolonged as a result of prolonged suckling period, nutritional deficiencies, climatic stresses, season, parity, suboptiomal
Ž .
Ž .
management and poor husbandry practices Eduvie, 1985 . Eduvie 1985 reported that postpartum ovulation occurred earlier in cows that had calved more than twice compared
to cows that calved two or less times. Calving intervals for cows calving in the dry Ž
season are shorter than for those calving in the rainy season Oliveira, 1974; Oyedipe et .
al., 1982 . Biostimulation is the term coined to describe the stimulatory effect of a male on
oestrus and ovulation through genital or pheromonal stimulation, or other less well-de- Ž
. fined external cues Chenoweth, 1983 . Pheromones are air-borne chemical substances
or AsignalsB released in the urine or feces of animals or secreted from cutaneous glands that are perceived by the olfactory system and that elicit both behavioural and endocrine
Ž .
Ž .
responses in conspecifics Doty, 1976 . The vomeronasal organ VNO is a bilateral blind sac that opens into the incisive duct or nasopalatine canal, and has been implicated
as a specialised chemoreceptor involved in the detection of oestrus and in the release, Ž
. control and coordination of sexual activity Estes, 1972; Wysocki, 1979; Johns, 1980 .
In domestic animals, priming pheromones from the male have an influence on the induction of puberty, the termination of seasonal anoestrus and shortening of postpartum
Ž .
anoestrus Izard, 1983 . Ž
. The duration of postpartum anoestrus in multiparous pluriparous and primiparous
Ž cows was decreased when cows were exposed to bulls following parturition Zalesky et
. al., 1984; Gifford et al., 1989 . The influence of a sterile bull on puerperium and fertility
in dairy cattle has been reported indicating that the use of a sterile bull could improve Ž
. fertility Ebert et al., 1972 . The first increase in progesterone, which indicated onset of
oestrous cycles occurred at 43 vs. 63 days postpartum in cows exposed and not exposed Ž
. to bulls, respectively Zalesky et al., 1984 . The same authors reported that a high
Ž .
percentage 89 vs. 18 of cows were detected in oestrus in the bull exposure than the
no exposure groups, respectively. The effect of a sterile bull on ovarian and behavioural activity of suckling beef cows indicated that in the group with the sterile teaser bull
present, the proportion of cows in which oestrus and ovulation was detected was higher Ž
. than in the control group Alberio et al., 1987 . The presence of a male causes more
intense stimulation, which decreases the rate of ovulation without expression of be- Ž
. havioural oestrus Ayalon and Weis, 1970; Ebert et al., 1972; Foote, 1974 .
Ž .
Effects of biostimulation exposure to bulls or testosterone treated cows on various reproductive variables in suckled cows indicated that cows exposed to bulls immediately
Ž after calving returned to oestrus earlier than cows isolated from bulls Burns and Spitzer,
. Ž
. 1992 . Recently, Bolanos et al.
1997 reported that bull and cow biostimulation
effectively enhanced resumption of ovarian activity in 60 anoestrus suckled zebu cows Ž
. Bos indicus in Costa Rica. The presence of the male stimulates postpartum reproduc-
tive activity, and that response can be modified effectively by the nutritional condition Ž
of the postpartum cows Alberio et al., 1987; Zalesky et al., 1984; Gifford et al., 1989; .
Monje et al., 1982; Stumpf et al., 1992 . Cows pastured with yearling or mature bulls initiated oestrous cycles 12 days earlier than cows isolated from bulls after calving,
indicating that biostimulatory effect of bulls on resumption of postpartum ovarian activity of cows is independent of the age of the bulls after they have reached 1 year of
Ž .
age Cupp et al., 1993 . There has been little or no documented information on the biostimulatory influences of bulls on resumption of postpartum ovarian activity in B.
indicus cattle. Therefore, the purpose of the present study was to determine the influence of bull biostimulation, season and parity on onset of postpartum ovarian function
following parturition in B. indicus cattle.
2. Materials and methods
