|Livestock Research for Rural Development 13 (6) 2001||
Citation of this paper
In order to verify the oestrus activity and to observe the body weight of Saanen goats, when reared in intensive condition of Northeast Brazil during four different seasons, ten adult Saanen goats were used. In this experiment four climatic seasons were considered; early rainy (ER), late rainy (LR), early dry (ED) and late dry (LD). Oestrus behaviour was monitored twice a day (8:00 a.m. and 4:00 p.m.) during all the experiment, using two vasectomised bucks. The oestrus cycles were quantified within each season and classified as short (< 17 days), normal (17-25 days) or long (> 25 days). The goats were weighed every seven days.
During the late rainy season, a significant fall of the mean body weight of the animals was observed when compared to early rainy season. A larger percentage of goats in oestrus were observed during the late rainy season. Oestrus duration was longer in the late rainy and early dry season than in early rainy and late dry season. During the experiment, there were 12.0% of short cycles, 50.3% of normal cycles and 37.7% of long cycles. The percentages of abnormal cycles (short and long cycles), in relation to total cycles monitored in each season were 52, 58, 38 and 50% for early rainy, late rainy, early dry and late dry, respectively.
results of this study it can be concluded that pen-fed Saanen goats do not show
seasonality for oestrus behaviour. Rainfall appeared to be an extero-receptive
factor influencing the quality of sexual activity and performance in these goats.
Brazil has 1.18% of the world goat population (FAO 2000) with 94% of them in the
Northeast region, confirming the great significance of
this region for goat production (IBGE
In northeast of
Brazil there is no clear policy for evaluating the local genotypes and
little appreciation of their potential. Thus emphasis has been on the importation of specialized
breeds, such as the Saanen, French Alpine and Toggenburg, the Anglo-nubian and Boer, which are maintained in their genetic
purity or used in crossings with local goat breeds. The Saanen
breed is the milk breed most widely used in the world for milk production and there are quite large
numbers in Brazil (Ribeiro 1997). There are reports of Saanen goats, exploited in the tropics, with exceptional production, such as the 3,084 kg
in 305 days of an Australian goat (Sands and McDowell 1978), confirming the productivity potential ability of this breed in the tropics. A
Alpine breeds originated in temperate countries, where they present sexual activity limited to a certain time of the year (Shelton 1978; Ortavant et al 1985; Chemineau et al 1992). In contrast, the native breeds of Northeast Brazil show sexual activity during the whole year (Silva Neto 1948; Simplício 1985; Simplício et al 1986). Therefore, the objective of this work was to verify the oestrous activity and to observe the body weight change of Saanen goats, reared intensively during four different seasons in tropical Northeast Brazil .
The experiment was carried out from April of 1998 to March of 2000 in the State
University of Ceará, Fortaleza, which is located at 3o 43'47 '' South and 38o
30'37 '' West. The variation of photoperiod in this location is
only 16 min between the solstices of the summer and winter.
The region where the experiment was carried out is
tropical and is characterized by small variation in annual
temperature (26 to 28o C). The highest rainfall is observed from January to June (FUNCEME 2000) (Figure 1).
In this experiment four climatic seasons were considered , which were described by Kronberg and Malechek (1997) as:
Ten adult Saanen goats were obtained from a private farm in
Fortaleza, where the conditions were similar
to those in the experimental location They were 15.6 ± 7.6 months old at the start of the experiment. In order to verify any reproductive disorder, ultrasonic
examinations (Shimasonic, 3 MHz probe) were performed monthly during the experiment.
Oestrus behaviour was monitored twice daily (8:00 a.m. and 4:00 p.m.) using two vasectomized bucks. Immobilization of the female when mounted by the male was considered to be a sign of occurrence of oestrus (Mauléon and Dauzier 1965). The number of oestrus cycles, as well as the length, were recorded during each season.The oestrous cycles were classified as short (< 17 days), normal (17-25 days) or long (> 25 days) (Chemineau et al 1992).
All calculations were performed
with the GLM of the SAS statistical programme (SAS 1995). Length of cycle (d), length of oestrus (h) and
body weight (kg) were submitted to two-way
analysis of variance. The data of length of cycle and length of oestrous were
transformed in log x. The following model of ANOVA was used:
yij = µ + ai +
ßj + eij
Yi j = observation;
µ = mean;
ai = effect of individual i;
ßj = effect of seasons j (j= ER, LR, ED, LD);
ei j = error term eij
Differences between means of body weights were identified by the Duncan test. Comparison between percentages was performed by Chi Square test. Results were expressed as mean± SEM and differences were taken as statistically significant at P<0.05.
Therainfall in Fortaleza during the experimental period was similar to the mean monthly value for 30 years (1961-1990), indicating that the experimental period was representative of the climate for this area. Two different seasons were identified, which present a length of six months each: rainy (from January to June) and dry (from July to December).
Figure 1: Mean
monthly rainfall (mm) in Fortaleza during the early rainy (ER), late rainy (LR), early dry
and late dry (LD) season from 1998 to 2000 (this experiment) and from 1961 to 1990 (FUNCEME 2000).
During the late rainy season, there was a significant decrease of the mean body weight of the animals when compared to the early rainy season (P < 0.05). During the early dry and late dry seasons, an increase (P<0.05) of body weight was observed (Figure 2).
Figure 2: Body weight
(mean ± SEM) of Saanen goats during the early rainy (ER),
late rainy (LR), early dry (ED) and late dry (LD) season
It was observed that all the goats showed oestrus behaviour throughout the experiment. However,
a larger percentage of goats in oestrus was observed during the
late rainy season (P<0.05), while in the other seasons the
percentage never exceeded 40% (Figure 3).
Figure 3: Mean percentage of Saanen goats in
oestrus, explored in tropical area,
during the early rainy (ER), late rainy (LR), early dry (ED) and late dry (LD) season
(ab: Different letters among seasons indicate a difference at P < 0.05)
Table 1: Mean and SEM for length of oestrus (hours) and length of oestrus cycles in the different seasons
Length of oestrus, hours
26.7 ± 2.54
34.9 ± 2.78
37.1 ± 3.48
28.4 ± 2.80
32.5 ± 4.34
33.2 ± 2.75
36.0 ± 3.45
37.6 ± 3.44
Length of cycle, days
18.3 ± 0.36
19.3 ± 0.3
19.6 ± 0.22
19.2 ± 0.53
The minimum length of oestrus found in the
experiment was 6h and the maximum 144 h. Season
had no apparent effect on the duration of oestrus nor on the length of the oestrus cycle (Table 1). The mean length of oestrus for
normal cycles, during the experiment, was 34.5 ± 1.69 h. The mean length of normal oestrus cycles was
The mean length of normal oestrus cycles was19.1 ± 0.35 days.
Alarger percentage of short cycles was observed in the late rainy season (P<0.05), when compared to the other seasons (Figure 4). Within the late rainy season, there were no differences in the percentages of short, normal and long cycles. In other seasons there were higher percentages of normal and long cycles compared to the short cycles (P<0.05). The minimum length of short cycle found was 2d and of long cycle was 305d.
Figure 4: Mean percentage of short, normal and
long oestrous cycles of Saanen goats,
during the early rainy (ER), late rainy (LR), early dry (ED) and late dry (LD) season.
ab Different small letters among types of cycles within seasons indicate difference (P<0.05).
AB Different capital letters for each type of cycle among seasons indicate difference (P < 0.05).
In tropical areas and below 25o latitude, the animal production is dependent
on the forage availability throughout the year
(Martin et al 1999). Overall, in the Northeast part of Brazil
and during the rainy season there is abundance of forage, while
during the dry season, the forage is scarce and fibrous and, consequently, of low quality
(Lindsay et al 1993).
The dry season in tropical areas is characterized by the low nutritive value of the natural forage. However,
the body weight of the goats in this
study increased in the dry season. In goats reared under grazing conditions, the browsing ability and the
characteristic of selecting the most nutritious parts of the plant allow them to change
their diet according to seasonal availability and growth rate of plants, and to increase
their dietary protein intake during dry periods (Louca et al 1982).
Seasonality of reproduction is a common feature in goat breeds of temperate latitudes,
as well as animals of the Saanen breed, and photoperiod seems to be the key factor
controlling reproduction in these areas (Shelton 1978; Ortavant et al 1985; Delgadillo
1990; Chemineau et al 1992). However, under tropical conditions, where the amplitude of
photoperiodic changes is lower, it is known that local breeds of goats are either
non-seasonal breeders or exhibit only a weak seasonality of reproduction (Chemineau 1986;
Simplício 1985). In this experiment, it was observed that the
highest rate of oestrus was in the late rainy season, which is characterized by the
In goats, the oestrus length is approximately 36 hours (Phillips et al 1943; Mishra and
Biswas 1966; Prasad and Bhattacharyya, 1979; Bliss 1980). Chemineau et al (1992) found a
mean length of 30 hours, for oestrus in Alpine goats submitted to the temperate and
tropical photoperiodic regimens. These data are in according with the results observed in
The high percentage of short cycles recorded
in the late rainy season was also reported by Cerbito et
al (1995) and Chemineau (1982), as being related to climatic factors, which act
as important cues in the reproduction of goats. Cerbito
et al (1995), working with native goats of Philippines, observed a
negative correlation between the length of the oestrous cycle and the rainfall. The
authors reported that a 76% increase in the rainfall corresponded to
a decrease in the same proportion in the length of the oestrus cycles.
Despite the high percentage of oestrus observed during the late rainy season, this fact cannot be related to a better reproductive activity, because during this season it was observed the largest percentage of abnormal cycles, mainly of short cycles. The short cycles in goats are related to poor ovulation quality (Camp et al 1983). Thus, we cannot translate the high percentage of oestrus verified in the late rainy season as a parameter of good fertility nor of good reproductive performance. The loss in body weight during the late rainy season could be the factor related to poor reproductive performance.
From the results of this study it can be concluded that pen-fed Saanen goats do not show seasonality for oestrus behaviour when raised in Northeast of Brazil. Rainfall appeared to be an extero-receptive factor influencing the quality of sexual activity and performance in these goats. Thus, goat-breeding programs in Brazil under intensive management could benefit from more extensive use of Saanen goats due to the minimal seasonal effects on reproduction.
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Received 14 July 2001
Received 14 July 2001
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