Effect Of Parity On Litter Size At Birth And At Weaning In Rabbits
Data on 100 litters from different parities were used to study the effect of parity on litter size at birth and at weaning in rabbits. The data were subjected to statistical analysis and the significant mean differences separated using student Newman Keul’s test. Traits considered were litter size at birth and at weaning. Results obtained showed that litter size at birth increased slightly from the 1st to the 2nd parity before declining with age. Litter size at birth in sixth parity was significantly different from those in other parities. Rabbit does with total number of litter size of five at birth had the highest percent occurrence of 24%. Also, rabbit does with total number of litter size of four at weaning had the highest percent distribution of 23% on the farm. The highest number of litter size at birth obtained was eight, the lowest was one and the average was approximately five. For litter size at weaning, the highest number obtained was seven, the lowest was one and the average was four. The predicted estimates showed that litter size at birth for the 1st and 2nd parities were generally slightly higher than for the 3rd to the sixth parity. This may suggest that 1st parity may be better in predicting doe performance than 3rd parity, although single records are not preferable in selection/culling policy.
1.1 Background of the Study
Owing to the increasing cost of animal protein sources in the developing Nations, leading to animal protein deficiency especially in Nigeria, it will be wise for farmers to embark on the production of livestock species which will give high protein turn over within a short period interval. Rabbit, a mini livestock fits into this description. All these benefits can be annexed with effective breeding programme such as selection of animals from reputable does and this should not be approached half hazard. It should be done from litters in parities that have proven to perform outstandingly. This study was therefore carried out to evaluate the effect of parity on litter size at birth and weaning in order to identify parities with higher litters. Selection on litter size has had a lower than expected success as a consequence of its low heritability (Baselga, 2014).
A reduction in the environmental variance of litter size would increase the heritability and consequently its response to selection. Besides, homogeneity in litter size reduces cross-fostering, facilitating management with a consequent reduction of costs. Pre-weaning mortality is a major cause of wastage in rabbit production. Filiz et al. (2015) stated that birth weight variation within litters affects kits survival and weight gain. Parity and litter size are some of the factors affecting birth weight. Milligan et al. (2012) indicated that parity influences birth weight and generally, does in first parity kindled litters with lower birth weight than does in other parities. Litter size at birth increases as parity increases. Yamani et al. (2011) reported that effect of parity on litter size at birth did not show any consistent trend. Litter size at weaning increased as parity advanced up to the sixth one. The differences in this character due to parity were significant (P ≤ 0.01).
Ouyed and Brun (2014) reported that rabbits from second parity were heavier at weaning (0.69 kg) and had the highest commercial carcass weight. This was in agreement with the result reported by Prayaga and Eady (2013). Litter size, parity and birth weight are some of the factors affecting survival rate. Higher litter size may cause elevation in mortality rate in first 10 days (Filiz et al., 2015). Recent studies have reported evidences for an additive genetic control of environmental variance on litter size (Sorensen and Waagepetersen, 2013) in pigs; (Gutiérrez et al., 2016) in mice and in uterine capacity; (Ibañez-Escriche et al., 2017) in rabbits, and in litter weight at birth (Garreau et al., 2004, in rabbits). According to Armero et al. (2015), litter size at birth and weaning have been the traits of choice to select specialized dam line. Parity have been reported to affect litter size which thus suggest that at some parities, litter size will be better than others.
1.2 Objectives of the Study
The objectives of this study are therefore:
- To determine the body weight of rabbits from different parities
- To determine the relationship between litter size and parity.
1.3 Significance of Study
Previous studies on nutritional strategies in pre- pubertal and reproducing females to stimulate energy intake and improve body condition during reproductive activity have not yielded appreciable results (Fortun-Lamothe, 1997, 1998; Xiccato et al., 1999; Pascual et al., 2002) whereas the application of less intensive reproductive rhythms has been shown more effective (Parigi Bini et al., 1996). Early weaning of litters has been proposed as a way to both reduce doe body energy output by decreasing the lactation period and ensure better coverage of kit nutritional requirements by separate kit and dam feeding (De Blas et al., 1999; Xiccato et al., 2000; Nicodemus et al., 2002).
This study was carried out to establish how doe parity order and litter weaning age can (1) affect voluntary energy intake and reproductive and lactation performance; (2) change doe body composition and energy reserves; and (3) decrease energy and tissue losses between kindling.
Discussion of Findings and Conclusion
Effect of the Parity Order
Studies on doe reproductive performance usually show a high fertility rate in nulliparous does, a lower fertility in primiparous does and intermediate values in multiparous does (Barge and Masoero, 1986; Rebollar et al., 1992; Castellini, 1995). The body energy deficit of primiparous does and the negative interactions between lactation and fertility have been considered the main reasons for these results (Theau- Cle´ment and Roustan, 1992; Fortun-Lamothe and Bolet, 1995; Parigi Bini and Xiccato, 1998; Fortun-
Lamothe et al., 1999). In our study, fertility was numerically higher in K3 does, but differences among parity orders were not significant.
As regards the relationships between parity order and reproductive traits, our results agreed with exist- ing literature describing greater litter size and weight at birth, and consequently lower average kit weight, with increasing parity order (Parigi Bini et al., 1989; Pascual et al., 1998; Szendro¨, 2000). We observed that kit survival was unaffected by parity order but litter weight at weaning and 32 days of age were stimulated by the higher milk production of does in their second and third lactation than of primiparous does, as also noted by Szendro¨ (2000). Despite the negative correlation with milk intake usually ob- served (Szendro¨, 2000), solid feed intake from 18 to 32 days of age was higher in the heavier litters of multiparous does. Differences in weight and probably also in digestive physiology development among litters from different parities may account for this result.
During the first lactation, chemical and energy changes confirmed previous results on primiparous lactating and concurrently pregnant does (Parigi Bini et al., 1992; Xiccato et al., 1992, 1995), where similar or even higher fat mobilisation (from 37% to 59% of the initial content) and energy losses (from 24% to 32% of the initial content) were recorded. The insufficient feed intake of primiparous does and the consequent inability to cover lactation and preg- nancy requirements are widely recognized as the main reasons for their body energy deficit (Maertens, 1992; Xiccato, 1996; Parigi Bini and Xiccato, 1998; Pascual et al., 1998). This is especially true in highly produc- tive hybrid rabbits, for which selection and cross- breeding strategies have been aimed at increasing prolificacy and milk production rather than voluntary feed intake and/or career length.
Unlike primiparous rabbits, multiparous does are usually considered capable of ingesting the higher amounts of feed required to achieve body energy and protein equilibrium. Partridge et al. (1983, 1986a) and Pascual et al. (2000), however, reported substantial body fat and energy mobilisation in multiparous lactating does. Various authors described significant increases (of 5 – 15%) in feed intake from the first to the second, and from the second to the third kindling, followed by lower but not significant increases for successive parities (Parigi Bini et al., 1989; Battaglini and Grandi, 1991; Castellini and Battaglini, 1991). In the present study as well, voluntary intake during lactation significantly increased with parity order. DE intake rose by 9% from K1 to K2 does, and only by 3% from K2 to K3 does. Milk production in- creased by 10 and 8%, respectively. The unchanged substantial gap between dietary energy intake and milk energy output accounted for the body deficit also maintained at higher parities. Pascual et al. (2000) found that non-pregnant does lost 16% of their initial fat content during second lactation. A total energy loss of 12.7 MJ was also calculated over 32 days of lactation in multiparous non-pregnant does fed ad libitum (Partridge et al., 1983).
On the basis of the energy requirement for maintenance and the coefficients of energy utilization for milk production and foetal growth reported by Parigi Bini and Xiccato (1998), the energy deficit for K2 and especially K3 rabbits should have been even higher than our findings. Other metabolic factors might have contributed to limiting the body energy deficit during the second and third lactation. According to Partridge et al. (1986a), fatter does (like our primiparous does) tended to mobilise body energy reserves for milk synthesis, while leaner does (like our multiparous does) tended to save body energy by either partitioning energy differently (e.g. decreasing milk energy output) or using dietary energy more efficiently. In this context, a lower milk energy concentration was found in leaner than fatter does by Partridge et al. (1986a) but no literature is available on the effect of parity order on milk composition.
In our study, protein seemed to play a secondary role in the energy balance of reproducing does, given that the experimental diets had an adequate digestible protein to DE ratio, and the digestible protein intake appeared sufficient to cover the protein requirement (Maertens, 1992; De Blas and Mateos, 1998). Previous studies showed the protein requirement to be higher during the last 10 days of pregnancy than during lactation and found limited body protein losses (5 to 10%) only in concurrently pregnant and lactating does subjected to intensive reproductive rhythm (Parigi Bini et al., 1992; Xiccato et al., 1995). Other authors have also reported a negative protein balance in non-pregnant multiparous does (Partridge et al., 1986b; Pascual et al., 2000).
The large variation in gut content that we recorded at initial and final kindling confirmed that live weight is a poor predictor of body tissue and energy changes, as stated by Partridge et al. (1983, 1986a). Gut content increased from the first to the second parity, as also reported in other studies (Parigi Bini et al., 1992; Xiccato et al., 1992, 1995), due to the marked reduction in feed intake a few days prior to first kindling, while prior to second kindling, feed intake decreased less, probably as a result of the lactation energy deficit (Lebas, 1972; Partridge et al., 1986b).
Effect of the Weaning Age
The feasibility of early weaning has been demon- strated in studies describing the good condition and survival rate of kits and the evolution of digestive physiology in kits and young rabbits (De Blas et al., 1981; Xiccato et al., 2000, 2001; Gutie´rrez et al., 2002). Our results confirmed a very low mortality of early weaned rabbits that had reached a suitable live weight (>550 g at 32 days of age). Moreover, the studies above report good performance during the growing period and similar slaughter weight in both early and traditionally weaned rabbits.
The main goal of early weaning is the reduction of doe body energy deficit, through the decrease of body energy utilization for milk synthesis by shortening the lactation length (period of energy deficit), and the increase of body energy restoration by prolonging the dry period (period of energy surplus).
Decreasing the lactation length undoubtedly reduces body energy output. Moreover, during the third decade of lactation (from 20 days onward), the simultaneous increase of milk dry matter and fat concentration (Lebas, 1971, 1972; Pascual et al., 1999) maintains the energy partitioned for milk production at a high level. In this period, however, daily milk production decreases while feed intake remains at maximum level or decreases only slightly for nearly a week, thereby making possible the achievement of the daily energy equilibrium or even a positive balance (Maertens and De Groote, 1988; Parigi Bini and Xiccato, 1998).
Prolonging the dry period increases the energy recovery time, as occurs when extensive remating rhythms are applied (Partridge et al., 1984; Cervera et al., 1993; Parigi Bini et al., 1996). However, the lower intake in the dry period compared to the lactation period reduces the daily energy gain and delays the complete restoration of body reserves.
In this study, voluntary feed intake decreased sharply from around 350 g/day prior to weaning to around 180 – 200 g/day within 4 – 5 days after weaning. In the first week after weaning, moreover, the W21 does showed a lower consumption (about 20 g/day) than the W26 and W32 does. The metabolic stress created by the sudden interruption of lactation in W21 does at top milk yield might have accounted for this feeding behavior.
On the basis of the measured milk production and feed intake of the does weaned at 32 days (average of the three parity groups) and the maintenance requirements and coefficients of energy utilization reported by Parigi Bini and Xiccato (1998), we estimated that the does were in positive balance for a few days after kindling before showing increasing energy deficits up to 0.8 MJ/day at 20 days of lactation. Due to the decreased milk production and stable feed intake from 20 days onward, the lactating does reached daily energy equilibrium at about 26 days. At 32 days, daily energy gain reached + 0.3 MJ/day and remained stable until the last days before kindling when it returned negative due to the increasing pregnancy requirement and decreasing feed intake. Partridge et al. (1986a) reported a similar change in body energy balance over a 32-day lactation period.
On the basis of the variation in daily balance described above, we calculated that W32 rabbits lost around 7 MJ from initial kindling to 21 days of lactation and a further 2 MJ from 21 to 26 days. Thereafter they gained around 1 MJ in the period from 26 to 32 days and another 1.5 MJ until 37 days, while the energy equilibrium was reached in the last 5 days before final kindling on average. From initial to final kindling, W32 does therefore lost around 6.5 MJ of body energy, primarily in the form of fat. For W21 and W26 does, the energy gain was estimated to be + 0.5 MJ/day in the first 5 days immediately after weaning and + 0.3 MJ/day onwards. Therefore, from initial to final kindling, W26 does lost around 5 MJ (= 7 2 + 2.5 + 1.5 + 0) and W21 does lost 1.5 MJ (= 7 + 2.5 + 1.5 + 1.5 + 0). The underestimation of the W21 doe energy deficit compared to the value measured by comparative slaughter (2.68 MJ) can be easily corrected by considering the lower feed intake of these does after weaning.
These calculations showed that increasing dry period length by early weaning permitted only a slow recovery of body energy reserves, due to the substantial decrease in post-weaning feed intake, and only partially prevented the occurrence of body deficit.
The significant interaction observed between parity order and weaning age showed only weaning at 21 days of age to be effective in reducing body deficits in does during the first-to-second kindling interval, but weaning at both 21 and 26 days of age improved the body condition of does during their second-to-third kindling interval. Early weaning did not efficiently reduce the doe body energy deficits during the third- to-fourth kindling interval. This interaction might be explained by the different evolution of the daily energy balance from one kindling to the next. In particular, on the basis of the model above and the different feed intake and milk yield curves, primiparous does seem to reach daily energy equilibrium at the end of lactation, and therefore only weaning at 21 days would reduce the energy deficit that remains high even during the entire third decade of lactation. On the other hand, does in their third lactation appear likely to reach daily energy equilibrium earlier (i.e. at 20 days of lactation) and achieve slightly positive balance during the third lactation decade. In such a case, early weaning would not substantially improve the total energy balance of multiparous does.
With no corroborating experimental reference, these initial results on the effects of early weaning on the doe body balance require further investigation. Reference data on the reproductive performance of does submitted to early weaning is also scarce. Nic- odemus et al. (2002) compared an intensive reproduc- tive system associated with early weaning (mating 4 days post partum and weaning at 25 days of age) with a traditional reproductive and weaning system (mating 11 days post partum and weaning at 35 days of age). Despite the fact that the effects of weaning age are closely linked to those of the remating interval, the authors observed significantly higher prolificacy and litter size at weaning in does mated 4 days post partum whose litters were weaned at 25 days than in does subjected to traditional rhythm. In light of our results, weaning age did not affect doe reproductive performance at final kindling, while the significant interactions measured with parity order are not easily explainable. The lower number of kits born and born alive per litter recorded in does at their fourth kindling whose litters were weaned at 21 days of age might be ascribed to the marked interference in the metabolic and hormonal pattern at the time of foetus implantation from 7 to 11 days of pregnancy (Fortun-Lamothe and Bolet, 1995), due to the sudden interruption of lactation in multiparous does with the highest milk production. In any case, the number of does in this study was insufficient to definitely evaluate these highly-variable reproductive traits.
This study confirmed the occurrence of body energy deficits in lactating and concurrently pregnant primiparous does and also measured substantial energy deficits in multiparous highly productive does. The dietary energy intake increased with parity order but was not sufficient to permit the complete recovery of body reserves lost during lactation even at the fourth kindling.
The feasibility of early weaning at 21 days of age was confirmed as indicated by the low mortality and suitable kit weight. Early weaning reduced doe body energy deficit by decreasing milk energy output but the sharp decrease in feed intake immediately after weaning delayed and limited the recovery of body tissue and energy. Moreover, early weaning at 21 days probably caused the does metabolic stress, as demonstrated by an even further decrease in feed intake and reduced reproductive performance, especially in multiparous rabbits.
In perspective, earliest weaning (21 days) should be limited to primiparous does, which are more susceptible to body deficit and less likely to suffer from metabolic stress caused by sudden interruption in lactation. Intermediate weaning (26 days) and less intensive reproductive rhythms might be used with multiparous does to overcome body energy deficits and avoid adverse effects on reproductive performance.
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