Comparison of Boer-Cross and foundation breeds for meat goat doe fitness in the humid subtropics

Athumani Nguluma, M L Leite-Browning* and R Browning Jr**

Institute of Agricultural and Environmental Research, Tennessee State University,
Nashville, TN 37209-1561, USA
asnguluma@yahoo.com
* Alabama Cooperative Extension System, Alabama A&M University,
PO Box 967, Normal, AL 35762, USA
** Institute of Agricultural and Environmental Research, Tennessee State University,
Nashville, TN 37209-1561 USA

Abstract

The aim of this study was to compare reproductive performance and health of Boer F1with Boer, Kiko and Spanish does. All does were mated by Myotonic bucks to produce crossbred kids.

Doe fertility was greater (P≤0.05) for Boer F1 (54%) than for purebred Boer (3.9%). More (P≤0.05)Kiko-sired does (56%) weaned kid than Boer-sired does (27%). Kiko-sired does weaned heavier (P≤0.05) litters (20kg) than Spanish-sired (16kg) and daughters of Kiko dams weaned heavier (P≤0.05) litters (20kg) than daughters of Boer dams (18kg). More (P≤0.05) Spanish-sired does (87%) stayed in the herd than Boer-sired (64%) through the first production year. More (P≤0.05) does from Kiko dams (90%) stayed in the herd than does from Boer dams (68%). At weaning Boer x Spanish does had lower (P≤0.05) gastro-intestinal parasite fecal egg count (FEC; 428 eggs/g) than Kiko does (1082 eggs/g). Kiko had positive direct genetic effects (P≤0.05) on fertility (38%) and  weaning rate (65%) while Boer had negative effect on fertility (-39%) and weaning rate (-74%). Heterosis was measured for fertility within the Boer x Kiko cross (23.9%). Crossbreeding with Boer did not (P≤0.05) improve doe productivity as Boer F1does were similar in performance to Kiko or Spanish, although improvement (P≤0.05) was seen over purebred Boer does.

Key words: crossbreeding, health, reproductive performance

Introduction

Profitability in meat goat farming depends to a large extent on the reproductive performance and health of animals. Meat goat breeds may differ in reproductive performance and health. Thus, it is important to identify breeds with optimum reproductive performance and health for the respective climate.

There is a wide range of breed choices for meat goat producers around the world. Introduction of a livestock breed into a production system should be done after scrutiny of the breed to ascertain its ability to compete with the indigenous breeds adapted to the local production environment. This has not been the case especially in developed countries where exotic breeds perceived to be more productive have replaced well adapted local breeds perceived to be inferior in production (Okeyo and Barker 2005).

Boer goats originate from the semi-arid regions of South Africa and they were developed through selection for high growth rate within the existing local populations (Casey and Niekerk 1988; Erasmus 2000; Malan 2000).There has been widespread use of Boer goat germ plasm in different parts of the world. The interest of meat goat producers in Boer goats is due to claims that they are fast growers, hardy and adaptable, resistant to diseases, fertile and produce meat of high quality (Casey and Niekerk 1988; Erasmus 2000; Malan 2000). Studies with the Boer goats in a wet and humid environment indicate that this breed is not as fit or productive as alternative Kiko or Spanish goats in the same environment (Browning et al 2004, 2011). The simulated performance of Boer and Spanish goats was compared under varying forage conditions (Blackburn 1995); comparisons did not favor Boer when forage conditions were moderate to poor.

The Kiko and Spanish are two alternative meat goat breeds available in the US. The Kiko was developed in humid regions of New Zealand through decades of crossbreeding feral does with European dairy bucks (Batten 1987). The Spanish is a landrace type that evolved through centuries of natural selection in the semi-arid regions of the present day southern United States and northern Mexico (Shelton 1978). Before the introduction of Boer and Kiko to the US in the 1990s, Spanish was the primary breed used for meat production. The infusion of Boer goats to the USA was expected to increase productivity through crossbreeding with or replacement of the resident Spanish goat.

Existence of differences in reproductive performance and health between crossbred and purebred females has been reported in different sheep and goat breeds (Bittante et al 1996; Mavrogenis 1996; Zaman et al2002; Okeyo et al 2005; Gaddour et al 2007). Similar studies involving Boer influence are not readily available in the scientific literature. The purpose of this study was to assess selected reproductive and health performance parameters of Boer F1 crossbred does relative to purebred Boer, Kiko and Spanish does.

Materials and Methods

Data for reproductive performance and health were collected from does born and raised on the Tennessee State University (Nashville, TN, USA) research station in 2007 and 2008. Does were derived from the mating of Boer, Kiko and Spanish does to bucks representing Boer (n=14), Spanish (n=11) and Kiko (n=13) breeds in a complete three-breed diallel mating scheme (Browning and Leite-Browning 2011). The genotypes of does used in the study included Boer (n=11), Spanish (n=30), Kiko (n=31), Boer x Kiko (n=19), Kiko x Boer (n=20), Boer x Spanish (n=16), and Spanish x Boer (n=25).  Spanish x Kiko reciprocal crossbred does were not retained for this study. The does representing the seven genotypes were bred to Myotonic bucks as a fourth, unrelated breed. 

The research station is 183 m above the sea level and found at 36.176°N, 86.828°W. This location is in the southeastern USA which is humid and has a subtropical climate with an annual precipitation of 1222 mm. Detailed description of the climatic conditions of the study location and animal management protocol were provided in the previous study (Browning et al 2011). Does were managed on pasture in which tall fescue (Festuca arundinacea) and bermuda grass (Cynodon dactylon) are the dominant forage species and they were supplemented with orchard grass hay (Dactylis glomerata). Water and minerals were provided for ad libitum consumption. Minerals given to animals were properly balanced with all necessary macro and micro elements. During breeding and from kidding to weaning, does were supplemented with 262g/d of a commercial concentrate (160 g CP/kg, 69% TDN ‘as fed’).

Does were nulliparous and 1.5 years old at mating. Mating occurred in fall and all does went into the breeding pens on the same date. At breeding does were weighed and fecal samples were collected. Does were subsequently assigned at random to Myotonic bucks in single-sire breeding pens for 30 days at ratio of 25 does to one buck. Bucks were equipped with a harness bearing a uniquely colored crayon to identify those does that were mated. After 1 month the original service sire was replaced with a cleanup Myotonic buck for 1 month.  

Does kidded on pasture in April2009 and March 2010. Within 24 hours after kidding, does and kids were weighed and kids were tagged and identified with their mothers. Stillbirths were not included in litter traits. Kidding does were dewormed at kidding after taking fecal samples. Male kids were not castrated and all kids were allowed to run with their dams up to weaning. All kids were weaned at once when the median kid age was 90 days. At weaning does and kids were weighed and fecal samples were collected from does. Does were monitored daily for clinical signs of lameness and internal parasitism. Clinical signs observed for internal parasitism were mandibular edema, diarrhea, anemia and lethargy. Additional dewormings and hoof treatments were provided individually for does showing signs of internal parasitism and lameness. 

Doe reproductive traits studied included fertility, weaning rate, prolificacy (number of kids born per does kidding), litter size at weaning (number of kids weaned per does kidding), total litter weight at birth and total litter weight at weaning. Fertility was measured based on the does kidding per does exposed and was coded as ‘zero’if a doe did not kid and ‘one’ if a doe kidded. Similarly the proportion of does weaning at least one kid per doe exposed was treated as a binary trait. Doe weight parameters studied included weight at breeding, kidding and weaning. 

Doe health was characterized by the following: proportion of does treated for lameness and internal parasitism, number of treatment cases and gastro-intestinal parasite egg count (FEC). Fecal samples were processed by the McMaster technique, a rapid, simple, quantitative technique for counting parasite eggs in ruminant feces, based on flotation on concentrated salt solution, at 50 eggs/g increments (Vadlejch et al 2011). Stayability was determined by assessing the proportion of does surviving to the end of their first production year. 

Data were analyzed using MIXED model analysis of variance procedures of the software SAS (SAS Institute, Carry, NC, USA). Two separate linear models (Model One and Model Two) were used to describe observations. Model One accounted for sire breed of the doe, dam breed of the doe and interaction between sire breed and dam breed of the doe as fixed effects. Model Two accounted for breed of the does. Model one was used to assess the influence of grand sires and grand dams on the performance of the particular breed. Calendar year, service sire, sire of the doe nested within breed and dam of the doe within breed and residue error were treated as random factors. Breed reciprocal crosses were assessed for Boer-Kiko and Boer-Spanish breed combinations. During data analysis the reciprocal crosses for each breed combination were grouped together to form one genetic group that was used as the main effect for model two. For analysis of doe weight and health traits, random effect of the service sire was removed from the models as they were irrelevant. 

The FECs were log transformed to normalize the data before statistical analysis and later back transformed and are reported as geometric means. Breed maternal and direct genetic effects and specific heterosis were computed based on linear contrasts for sire breed and dam breed of the doe using Model One. Due to small sample size and very low reproductive output of Boer does it was not possible to estimate breed genetic effects and specific heterosis for all reproductive traits. The Tukey-Kramer means separation test was used for comparing least square means for all doe traits. Probability levels equal to or less than 0.05 (P≤0.05) for the F-statistic was used to indicate statistical significance of the main or interaction effect unless otherwise noted as a tendency (0.05≤P≤0.10).

Results

Doe weight parameters.

Least squares means for weight parameters are presented in Table 1. All sources of variation considered to affect doe weight at breeding were significant except sire breed of the doe. Daughters of Kiko dams were heavier at breeding than from Boer and Spanish dams. Dam breed of the doe was the only effect on body weight at kidding. Daughters of Kiko dams were heavier than from Spanish dams. There were no sources of variation for doe weight at weaning.  

There was interaction in doe weight at breeding between sire breed and dam breed of the doe. The interaction was because Kiko dams within Boer sires had greater daughter weights at breeding than Boer and Spanish dams. 

 Kidding and weaning rate

Kidding rate was affected by dam breed of doe, sire breed of doe and doe genetic group. Kidding rates for Boer F1 does were greater than for Boer but did not differ from Kiko and Spanish does (Table 2).Daughters of Boer sires had the lowest kidding rate and were different from daughters of Kiko and Spanish sires. Daughters of Kiko dams had greater kidding rate than daughters of Boer dams but not different from daughters of Spanish dams.

Weaning rate differed among sire breed of doe, dam breed of doe and doe genetic groups. Boer F1 crossbred does did not differ from their foundation breeds (Table 2). However Boer does had lower rates than Kiko and Spanish does. Daughters of both Kiko sires and dams had greater weaning rate than of Boer sires or dams (Table 2). Daughters of Spanish sires and dams did not differ from daughters of Boer and Kiko sires or dams.

Litter traits at birth and at weaning. 

There was no genetic effect on litter size at birth, litter size at weaning, or litter weight at birth when sire breed and dam breed of the doe and doe genetic groups were considered as sources of variation (Table 3).Doe genotype affected litter weight at weaning. Litter weight at weaning was found to be heavier for purebred Kiko does compared to Boer x Spanish F1 does (Table 3).  Boer x Kiko F1 and Boer x Spanish F1 does did not differ from their respective foundation Kiko and Spanish purebred cohorts. Sire breed and dam breed of the doe affected litter weight at weaning. Daughters of Kiko sires had heavier litters at weaning than those of Spanish sires. Daughters of Kiko dams had heavier litters at weaning than those of Boer dams. 

Doe health parameters

Crossbred does did not vary from purebred does for internal parasite treatments (Table 4).There was a tendency (P=0.068) for fewer Kiko does to be treated for internal parasitism than Boer does.Doe stayability up to the end of their first production year was affected by sire breed of the doe and dam breed of the doe. Daughters of Kiko dams had greater stayability rates than those of Boer dams and daughters of Spanish sires had greater stayability rates than those from Boer sires. Kiko purebred does tended to have higher stayability rates than purebred Boer does (Table 4). No difference was found among genetic groups and sire breed and dam breed of the does for episodes of treatment and proportion of does that were treated for lameness. 

Genetic groups tended to differ for FEC at breeding and at weaning (Table 5). Boer F1 did not differ from any of their foundation parents in FEC at breeding and at weaning. Boer does tended to have higher FEC at breeding than Kiko and Spanish does. At weaning Kiko does had greater FEC than Boer x Spanish crosses but not different from other genotypes. Boer F1 does did not differ from respective foundation breed does for FEC. Sire breed and dam breed of the does did not have a significant effect on FEC at breeding or weaning. 

Breed additive genetic estimates on reproductive and weight parameters

Table 6 shows the breed additive genetic effects and specific heterosis for weight and reproductive traits. Breed direct effect on doe weight at breeding was significant for Kiko while estimates for breed maternal effects were significant but negative for Boer and positive for Kiko. Estimates for breed direct effect on kidding rate were all significant and positive for Kiko and Spanish while negative for Boer. Breed maternal effect estimates were not important. Specific heterosis for kidding rate was positive and significant only for the Boer x Kiko cross. All estimates for breed direct, maternal effects and individual heterosis for lameness, internal parasitism and stayability were found not to differ from zero. 

Discussion

Doe weight parameters

Crossbred does did not differ from Kiko and Spanish does for weight at breeding. In contrast, Rhone (2005) reported Boer x Spanish does to be heavier at breeding than Spanish does. In his study however the influence of Boer as a dam breed and Spanish as a sire breed was not assessed as he did not have Boer x Spanish reciprocal crosses. Boer x Kiko crossbred does were heavier at breeding than Boer does in the current study. The positive direct and maternal genetic effect of Kiko contributed to this superiority in weight at breeding of the Kiko crosses. Browning and Leite-Browning (2011) reported maternal genetic effect on weaning weight to be positive for Kiko and negative for Boer. Does in the study were part of the larger kid population of Browning and Leite-Browning (2011) and maternal effects documented at weaning may have persisted to influence weights of the does a year later at breeding.

Reproductive performance

The proportion of doe mating resulting in at least one live kid at birth is a measure of fertility. Boer F1 does had greater fertility than purebred Boer does but similar to Kiko and Spanish. This lack of difference between Boer F1 and purebred Kiko and Spanish does agrees with studies on Boer x Feral, Boer x Angora, and Boer x Spanish crossbred does compared to purebred Feral, Angora, and Spanish does (Norton 2004; Rhone 2005). The paternal line of Boer germ plasms showed poor performance as evidenced by the lower fertility of daughters of Boer sires than daughters of Kiko and Spanish sires and the negative direct genetic effect of Boer on fertility. Fertility values observed in this study were lower than rates reported previously (Norton 2004; Rhone 2005; Browning et al 2011). In the current study all does were nulliparous yearlings when buck exposed which could have contributed to relatively lower fertility rates. Unlike for kidding rate, crossbreeding did not result in weaning rate sbeing greater for Boer F1 does than for purebred Boer does; weaning rates for Boer F1groups were under 50%.

Similar to the current results for Kiko and Spanish relative to their Boer crosses, Rhone (2005) found no difference in prolificacy of Boer x Spanish and Spanish does. No difference in prolificacy was expressed among Boer x Angora and Angora, Boer x Feral and Feral, and Boer x Saanen and Saanen does (Norton 2004).  Differences in prolificacy between purebred and crossbred female have been reported among other goat breeds not involving Boer (Zaman et al 2002); this study used the highly prolific Black Bengal to improve a non-prolific breed. Due to the poor fertility of the Boer does in the current study, prolificacy comparisons could not be made between purebred Boer and their crosses with Kiko and Spanish. However in previous work done at this location, Browning et al (2011) reported the prolificacy of Boer to be 1.83 ± 0.12 kids, similar to Kiko and Spanish across six years.

Litter size at weaning per does kidding as a doe trait is a collective measure of prolificacy of the doe and survival of kids up to weaning. The latter can be influenced by mothering ability of does. Boer F1 did not differ from other doe genotypes in prolificacy; therefore lack of difference among genotypes for litter size at weaning indicates that Boer F1 in this study failed to express any significant difference from their foundation Kiko and Spanish cohorts in mothering ability necessary to successfully raise kids to weaning. This would be expected also considering the high negative direct effect of Boer on weaning rate. Boer does however were not included in analysis of this trait due to poor kidding rate that did not allow any calculation based on litter traits. In a previous study at this location, litter size per doe kidding was significantly lower for purebred Boer does than for purebred Kiko and Spanish does (Browning et al 2011).

Litter weight at birth did not differ between Boer F1 and their foundation Kiko and Spanish parental breeds. Rhone (2005) made a similar observation for Boer x Spanish and Spanish does. Among non-Boer crosses, German Fawn x local Katjang F1had higher litter weight at birth than purebred local Katjang does (Tsukahara et al 2007).In sheep, Mavrogenis (1996)found litter weight at birth of Chios x Awassi crossbred ewes to be significantly higher than that of Awassi purebreds.  The two latter studies showed that litter weight at birth was positively related to high prolificacy or high growth potential of one of the breeds used in the cross. Lack of difference in litter weight at birth in the current study is likely associated with the lack of divergence among Boer, Kiko and Spanish for prolificacy.

Litter weight at weaning has major economic importance in meat goat production. In the current study Boer F1 does did not differ from either of their respective Kiko or Spanish parental breeds. Due to poor kidding rate of the Boer does, direct and maternal genetic effects of the breeds involved in the cross could not be estimated. However, Kiko germ plasms exhibited an advantage as both a sire breed and dam breed for litter weight at weaning; daughters of Kiko sires over Spanish sires and daughters of Kiko dams over Boer dams. In another study (Rhone 2005) Boer x Spanish and Spanish does had similar litter weights at weaning. Litter weight at weaning between purebred Small East African does and crosses of Small East African with Anglo-Nubian and Alpine goats did not differ (Trevor and Murray 1988).  Higher litter weight at weaning can be due to higher litter size at weaning or higher weaning weight of individual kids. In a crossbreeding experiment involving D’man and Sardi sheep breeds (Boujenane and Bradford 1991), F1 crossbred ewes had higher litter weights at weaning than both purebred parents. The superiority of the crossbred ewes in litter weight depended on litter size. When enhanced total litter weight at weaning is the primary focus of production, Boer crossbred does did not demonstrate improved performance over Kiko or Spanish purebred does.

Doe health parameters

Boer F1 and Boer does did not differ for internal parasitism and FEC despite large numerical differences. Small sample sizes would likely account for the non-significance. However, Boer does had almost twice the number of treatment for internal parasitism than Boer F1. Boer does exhibited greater internal parasitism and lameness occurrences than Kiko and Spanish in a larger dataset of purebred does (Browning et al 2011). Kiko does did have lower treatment rates for internal parasites than Boer does in the current study. Unlike in the current study which revealed no difference between Boer F1 and Boer does for lameness, Boer crosses with Alpine, Saanen and local Tunisian goats had reduced lameness treatment cases compared to purebred Boer (Steinbach 1988); Boer goats had close to 200 veterinary treatments per 100 goats per year while crossbreds had less than 50 treatments.  In an outbreak of foot rot in Israel, East Friesian × Awassi crossbred sheep were less affected than purebred Awassi (FAO 2006).

In the current study doe exits from the herd were mainly due to deaths associated with internal parasitism. Crossbreeding did not improve stayability of Boer F1 over their purebred contemporaries. Among purebreds, Boer does had lower stayability rate than Kiko does, in agreement with Browning et al(2011); the previous study also found stayability to be greater for Spanish than for Boer. These breed relationships for stayability were also reflected in the sire breed and dam breed comparisons here, both of which reflected poorly on the Boer contribution. Consistent with results in the current study, Rhone (2005) reported no difference in the rate of does leaving the herd for different reasons between Boer x Spanish F1 and Spanish does. To the contrary, Boer x Small East African crosses tended to have greater rates of leaving the herd than purebred Small East African goats due to susceptibility of Boer to diseases caused by their poor adaptation to harsh environment (Mtenga et al 1992).

Conclusions

• Crossbreeding with Boer to generate hybrid does did not prove to be a valuable option in enhancing meat goat herd performance under the conditions of this study. In the current study the expected advantage of Boer crossbred does in body weight was not evident. Increased nutritional, health and labor requirements associated with Boer goats may be the reason for the lack of weight advantage. There was no evidence in support of using Boer F1 does in place of Kiko and Spanish purebred does in a semi-intensive goat production system for enhanced reproductive performance. This outcome is supported by the past studies at this research location consistently showing purebred Boer females to be inferior to Kiko and Spanish females for fitness traits under limited-resource conditions.

• Boer germ plasm has been widely used with the expectation of increased animal weight over unimproved goats such as Spanish. The Spanish goat is typical of local, indigenous, unimproved goat populations found throughout the developing world. Use of breeds regarded as superior for upgrading local breeds has been done in many regions without studies to scrutinize the ability of the breeds to survive and remain productive in the particular environment.Use of Boer germ plasms for improving the purportedly local inferior breeds in such areas should be viewed with caution.

Acknowledgement

The first author wishes to thank Tanzania Livestock Research Institute-West Kilimanjaro where he is currently working for granting him study leave that gave him time to conduct the research.  The authors express appreciation to A Pellerin, J Groves and M Byars for assistance in herd management.

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Received 23 November 2012; Accepted 7 December 2012; Published 1 March 2013

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