www.elsevier.comrlocaterapplanim
Mating behavior of bucks and does in goat
operations under range conditions
Miguel Mellado
), Crispina Cardenas, Fernando Ruız
´
´
Department of Animal Science, UAAAN, Saltillo, Coahuila, MexicoAccepted 2 November 1999
Abstract
The objectives of this study were to characterize the mating capacity of bucks under range condition and assess the effect of mating frequency on flock fertility. Two adjacent flocks of
Ž .
crossbred goats Criollo=dairy breeds; ns70 does, 5 bucks and 141 does, 4 bucks were used in this study. The mating period was 16 and 20 days for each flock, respectively, in January and February, 1996. Mating activity of bucks and does was recorded day and night during the first 11 days of the breeding period. The combined data of both flocks showed a strong relationship
Ž .
between number of goats in estrus and the average services of bucks rs0.95; P-0.01 . With an excess of estrous does, bucks on average copulated 9.1 times daily during the first 11 days of the mating period. Considering both flocks combined, does copulated on average 4"1.8 times through the estrus period, and they did so with an average of 2.2"1.3 different bucks. Sexual activity of bucks was greatest from sunset to midday. Number of services from different bucks did
Ž
not affect pregnancy rate 81.4% for goats serviced by 1–2 bucks and 77.8% for goats serviced by
2 .
3–4 different bucks; x s0.25; P)0.05 . Also pregnancy rate was not influenced by total Ž
number of services 81.3%, 75.0% and 81.4% for 1–3, 4–6 and )7 services, respectively;
2 .
x s0.67; P)0.05 . Mean"S.D. daily liveweight loss of bucks during the entire mating period was 547"197 g. It was concluded that, with buck percentages higher than 3%, the number of ejaculations of bucks is linearly and positively related to number of females in estrus. Also, these findings indicate that neither number of copulations nor number of services from different bucks affected kidding rates.q2000 Elsevier Science B.V. All rights reserved.
Keywords: Goats; Sexual behavior; Reproduction; Fertility
)Corresponding author. Tel.:q52-84-17-30-22 ext. 350; fax:q52-84-17-61-11.
Ž .
E-mail address: mmelbos@uaaan.mx M. Mellado .
0168-1591r00r$ - see front matterq2000 Elsevier Science B.V. All rights reserved. Ž .
1. Introduction
Practically 100% of pregnancies in the goat operations in Mexico derive from natural mating. Despite this, the breeding ability of bucks is never considered, and it is assumed that the buck will perform satisfactorily at any time and under any buck:doe ratio. In the
Ž .
arid ranges, bucks cover great distances per day during the short 10–30 days breeding season, in search of does exhibiting estrus, therefore they undergo a significant physical stress during this period, especially in cases of a large buck:doe ratio, high ambient temperatures and sites of sparse vegetation. Under these circumstances several aspects of buck sexual behavior, such as mounting activity throughout the day, ejaculation fre-quency, libido, and variation in body weight constitute important pieces of information to design a reproductive program for bucks under range conditions. These aspects of sexual performance have received a relatively great deal of attention in bulls and rams, but not in bucks. Also it is unknown to what extent these behaviors contribute to reproductive success. Thus, the objective of this study was to characterize the sexual behavior of bucks during both daylight and dark hours, during a short mating period in a goat operation under range conditions. A further objective was to determine the effect of mating frequency on flock fertility.
2. Material and methods
2.1. Study flocks
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Two adjacent flocks of crossbred goats Criollo=dairy breeds were used in this
Ž X X
.
study. The goat operations are located in northeast Mexico 25807 N, 101840 W , at an
altitude of 2150 m above sea level. Mean annual temperature is 168C and average annual
Ž precipitation is 299 mm. Goats grazed on desert grassland during 8 h daily 1000 to
.
1800 h , and were penned from 1800 to 1000 h, with no extra food or salt supplementa-tion. Both flocks spent the night in unroofed corrals made of shrub branches. The predominant species in this zone are Yucca carnerosana, Nolina microcarpa,
Dasilir-ium cedrosanum, AgaÕe lechuguilla, Partheniun incanun, Bouteloua curtipendula, Bouteloua gracilis, Stipa leucotricha and Aristida diÕaricata. Goats had access to water
only once a day.
2.2. Experimental protocol
In one of the flocks, three adult Nubian and two Granadino bucks having a body
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condition score of 6 BCS; 1sthin, 9sobese , and with previous mating experience
were exposed to 70 goats during 16 days in January 1996. The bucks averaged 69.1 kg
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body weight S.D.s9.2 kg at the beginning of the mating period. In the other flock,
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two mature Granadino and two Nubian bucks with a mean BW of 56 kg S.D.s13.7
.
However, during the daily observation of bucks, no health, structural, or reproductive soundness problems were observed among bucks.
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Buck activity was continuously monitored day and night, in the pen and in the open .
range from days 1 to 11 of the mating period. Observations were made by four observers: two in the day and two at night, with spotlights, throughout the observation period.
In both flocks the number of does in estrus and the number of services completed by each buck was registered every day. Only in the largest flock were recorded the time when the services took place and the occurrences of abortions and kiddings. Pregnancy rates were calculated from the kidding and abortion data. The criteria used to define a service was a mount that culminated in a strong pelvic thrust, with observation, when possible, of fully extended penis when withdrawn from the doe’s vagina. The number of services received by each doe was also recorded. In both flocks bucks were weighed at the beginning and end of the mating period. From these observations the following
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parameters were selected for the analysis of sexual behavior patterns: 1 average
Ž . Ž .
ejaculations received per estrous doe, 2 total ejaculations of bucks per day, 3 percent Ž .
of does kidding or aborting to observed matings, 4 time of the day when copulations Ž .
took place, 5 number of does in heat per day.
2.3. Statistical analyses
A linear regression was used to analyze the association between number of goats in heat in a specific day and the average number of buck services. The same procedure was used to assess the association between total number of copulations and average daily liveweight loss of bucks. A frequency table was used to describe the mating activity of
bucks throughout the day. Differences in fertility between groups were tested using x2
procedures.
3. Results
3.1. Mounting behaÕior as a function of goats in heat
Ž .
The frequency of services average of all bucks in relation to the number of goats exhibiting estrus is presented in Fig. 1. A test for coincidence from separate straight-line regression fits indicated that regression coefficients and intercepts were constant over flocks, therefore data of both flocks were combined in a single regression analysis. A
Ž .
strong association rs0.95; P-0.01 was found between availability of goats in heat
and buck’s services. With an excess of estrous does, bucks on average copulated 9.1 times daily during the first 11 days of the mating period. There was ample variation in number of matings among bucks. The most active buck copulated 155 times in 11 days, whereas the least active buck mated 32 times in the same period of time. Considering
both flocks combined, does copulated on average 4"1.8 times through the period of
Fig. 1. Mean number of services with respect to number of does in heat, during the first 11 days of the mating period.
Table 1
The effect of total number of copulations and number of services from different bucks, on pregnancy rate of goats under range conditions
a
Ž .
Services received Number of goat mated Goats impregnated %
1–3 48 81.3
Fig. 2 shows the distribution of copulations throughout the day. The services during the daylight hours comprised 64.4% of the total services occurring during a 24-h period.
Ž . Ž .
The majority of copulations 59% occurred in pen 1800 to 1000 h .
Because of the great proportion of time engaged in sexual activity, bucks expend very little time eating during the mating period, which led to a severe loss of weight of these
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animals mean"S.D. liveweight loss during the mating period was 9.6"3.2 kg . Total
Ž
number of services was negatively though non-significantly associated rs y0.27;
.
P)0.05 with daily liveweight loss.
3.2. ReproductiÕe performance of does in relation to copulation actiÕity
Pregnancy rates as a function of number of copulations from different bucks and total number of inseminations received by does during the heat period is presented in Table 1.
Ž 2 .
Neither number of services from different bucks x s0.25; P)0.05 nor total
Ž 2 .
number of ejaculations received during the heat period x s0.67; P)0.05 affected
pregnancy rates.
4. Discussion
This study shows clearly that there is a strong relationship between the number of goats in estrus and number of times bucks ejaculate each day. Regression of average number of matings on availability of does in estrus was 0.76 copulations per day. This essentially shows that, with an uninterrupted availability of does in estrus during the mating period, for each additional goat in heat in a specific day, bucks are expected to have nearly one additional service. These results support the hypothesis that under field conditions the number of ejaculations of bucks is linearly and positively related to number of females in estrus. The increase in mating activity of males with increased
Ž
availability of females in heat also has been documented in sheep Hulet et al., 1962a; Tompkins and Bryant, 1972; Shreffler and Hohenboken, 1974; Allison, 1975; Synnot et
. Ž
al., 1981 . However, with mating loads less than 1% of rams greater number of does in .
because males work at peak activity and therefore are unable to increase service rates
ŽFowler, 1982 . Thus, with higher breeding pressure it is possible that the relationship.
between number of goats in estrus and number of ejaculations might be curvilinear, approaching some theoretical asymptotic value indicative of a male’s maximum ejacula-tory capacity.
It can be argued that bucks regulate their breeding activity so that their spermatozoa reserves are not easily depleted. Also, It could be that, with a limited number of does in heat, the bucks limit their copulation rate in order not to risk the doe ejecting part of his earlier ejaculation. Similar to what was reported to happen in sheep, these data also indicate that the number of times each doe is mated tended to remain fairly constant, regardless of the number of does in heat.
The copulation frequency of individual goats varied from 1 to 19 during the estrous period, and practically all goats were serviced by more than one buck. Due to the high frequency of services of bucks, which results in reduced densities of sperm in ejaculates
ŽLightfoot and Smith, 1968; Synnott et al., 1981 , does might seek repeated copulations.
in order to compensate for ejaculates containing few sperm. Also does may seek different bucks during the estrous cycle in order to get a heterogeneous population of spermatozoa, which would assure a reservoir of viable gametes. This may explain the behavior of does in heat which tended to group around different bucks soliciting copulation more than once. On the other hand, due to the heterospermic natural insemination of most does, the frequent copulation by bucks could be a strategy for gaining paternity when the sperm of one male is in competition with that of another. The high number of ejaculates received by each doe show that the mating capability of bucks has been underestimated. Bucks performed an average of 9.1 copulations daily, and if
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able to maintain this during a short breeding periods less than 1 month some bucks would be capable of impregnating around 100 does during the course of one estrous cycle. Thus, under range conditions and with the typical buck to doe ratio used in
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commercial flocks of northern Mexico no more than 2% bucks , it seems to be a waste of the breeding potential of bucks. It appears that bucks can be subjected to higher
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breeding pressure, as it has been shown by Mellado et al. 1996 who found that mating loads of 1 buck per 50–75 does did not compromise kidding rate of goats under range conditions.
Ž
Similar to other studies with rams Hulet et al., 1962b,c; Mattner et al., 1967; .
Blockey and Cumming, 1970; Kilgour, 1993 , sexual activity of bucks was greatest from sunset to midday. The mating period in this study took place during the coldest part of
Ž
the year, thus the highest sexual activity occurred with mild temperatures 10–208C
.
during the day . This pattern of sexual performance may not be the same during the
summer, when maximum temperatures in this zone are around 358C.
Forty-one percent of the copulations occurred on range, which indicates that the dispersion and movement of the flock while feeding did not limit the copulation activity of bucks. Also, 36% of matings took place during the dark hours, which indicates that bucks exhibited a desire to mate at any time of the day.
Bucks lost 547 grday during the mating season. This loss of weight is much higher
Ž
than that reported in rams by other authors Combrink and Schoeman, 1993; Gizaw and .
ones in the present study. These findings underscore the importance of a good body condition for bucks when mating takes place on range during the dry season.
In this study there was no significant differences in pregnancy rate in does bred by few or many different bucks. Likewise, total number of services received did not affect number of does impregnated. Because of the high percentage of bucks in the flocks of this study, most does were mated by more than three different bucks and copulated repeatedly during the heat period, therefore in most cases does probably received an excess of heterogeneous spermatozoa. Therefore, differences in total number of copula-tions or number of bucks mating each doe were not large enough to affect flock fertility. With much higher mating loads it has been documented that higher lambing rates occur
Ž .
when ewes are mated by two or three rams as compared to only one Allison, 1975 . Also, it has been recorded that ewes inseminated more than once have a greater chance
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of conception Mattner and Braden, 1967; Robinson, 1970 .
5. Conclusion
From these data it was concluded that, under range conditions, number of copulations per doe tended to remain fairly constant regardless of the number of does in heat, which means that an increase in number of does in heat is accompanied by an increase in the number of copulations per buck per day. Also, these findings indicate that neither number of copulations nor number of services from different bucks affected pregnancy rates.
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