Productive response of hair ewes crossed with Damara and Dorper and growth of their lambs

Profitability of sheep production depends on the reproductive response of ewes and growth of their lambs, which can be improved through the ram genotype. The aim of this study was to evaluate the reproductive response of Blackbelly (Bb), Pelibuey (Pb), Katahdin (Kat) and Dorper (Dor) ewes crossed with Damara (Dam) and Dor rams and the growth of their offspring. To measure percentage of single and multiple lambings (MLP), 234 Bb, Pb, Kat and Dor ewes were used. To measure lamb growth, the offspring of 86 Bb x Pb (BbPb) ewes and 73 Kat x Dor (KatDOR) ewes were used. Four Dor x BbPb, six Dam x BbPb and six Dam x KatDor lambs were slaughtered for carcass assessment. MLP was analyzed with the CATMOD procedure considering the factors age and breed. Lamb growth data were analyzed with the MIXED procedure, and those of carcass characteristics with the GLM procedure of SAS, using weight at slaughter as covariable. MLP was higher (P<0.05) in Bb than in Dor. The Dor x BbPb lambs were heavier (P<0.05) at birth than Dam x BbPb. Of the lambs from single and multiple births, the KatDor lambs were heavier (P<0.05) at birth than BbPb lambs. The female lambs of Dor rams had higher (P<0.05) weight gain after weaning than those of Dam rams. Carcass dressing, subcutaneous fat, and primal cut yield were not different (P>0.05) by effect of ram breed. It is concluded that Bb ewes are more prolific than Dor ewes; male lambs of Dam rams had post-weaning growth response and carcass yield similar to those of Dor rams, although the female lambs of Dor rams were heavier than those of Dam rams.


INTRODUCTION
Reproductive characteristics, body growth and meat yield determine rentability of a sheep production unit, for which the ram and ewe breed is determinant.Regarding the ewe, Blackbelly (Bb) and Pelibuey (Pb) are prolific breeds adapted to tropical conditions, but their growth rates are low (González et al., 2002;Macedo and Arredondo, 2008).Dorper ewes achieve daily weight gain of 240 to 280g under different environmental conditions (Cloete et al., 2000), while Katahdin ewes are outstanding for their good productive response in terms of the number of live-born lambs and meat production.Crosses with Dorper (Dor) and Katahdin (Kat) breeds have been used to increase meat production.Regarding the ram breed, crossing hair sheep ewes with Dor rams results in offspring with better weight gain (Macías-Cruz et al., 2010), while crossing Damara (Dam) rams with Merino ewes increases weight gain of their lambs at five months of age, relative to those of pure Merino (Fleet et al., 2002).The Dam breed has been introduced in Mexico due to their rusticity, maternal skill and ability to cover long grazing distances, but there are no studies on the productive response of their offspring when they are crossed with hair sheep ewes.For this reason, the aim of this study was to assess the percentage of multiple births of Kat, Dor, Pb, and Bb ewes and lamb growth and carcass characteristics of the offspring when they are bred with Dam and Dor rams.

MATERIALS AND METHODS
The study was conducted in a privately owned flock in Tlacolula, Oaxaca, located at 6° 57' N, 96° 28' W and altitude of 1620m.The climate is dry steppe, with a mean annual temperature of 18ºC (García, 1998).
The percentage of multiple lambings was calculated with 234 records of ewes of the breed groups Bb, Pb, Dor, and Kat, which were classified into groups of younger or older than 4 years of age.The ewes were confined during the night and grazed on Banderita (Bouteloua curtipendula) and Buffel (Cenchrus ciliaris) grass and Huizache (Acacia farnesiana) trees.During periods of scarce forage, they received 300g d -1 growth concentrate (Tab. 1) and bean and maize harvest residues and alfalfa hay.The ewes mated in continuous breeding year round with Dam or Dor rams.Thirty days before lambing they were kept in confinement and received 400g d -1 lactation concentrate (Tab.2) and had free access to maize and bean harvest residues and alfalfa hay.Lambing occurred from January to July and was classified as single or multiple (two or more lambs born alive).
The effect of ram breed and ewe race group on birth weight, weaning weight and post-weaning weight gain of the lambs was determined with a second lot of ewes two to four years old, crosses of Pelibuey x Blackbelly (BbPb, n=86), and of Katahdin x Dorper (KatDor, n=73) 20 days after weaning.The ewes received 10mg of ivermectin 50kg -1 live weight and 3 days later they were synchronized with an intravaginal device (CIDR ® ) for 12d.When the device was removed they were administered 250IU intramuscular PMSG.Twenty-four h after withdrawing the CIDR, estrus was detected with rams covered with an apron.The ewes were mated in the same proportion with purebred Dor (n=4) and Dam (n=4) rams.Four types of crosses resulted: Dam x BbPb, Dam x KatDor, Dor x BbPb, and Dor x KatDor.During synchronization 0.5kg d -1 concentrate was offered to each ewe; the concentrate contained 13.42% CP and 2.76Mcal kg -1 EM.The ewes were housed in corrals where they were given free access to water, maize and bean harvest residues and alfalfa hay.Two weeks before parturition and until weaning, the ewes were housed in corrals where they were given 300g d -1 lactation feed, forage (maize and bean harvest residues and alfalfa hay) and free access to water (Tab.1).The corrals have trap pens which only lambs can access, and as of 15d of age the lambs were given feed (Tab.1).Weaning was done at 65d of age, and for 15d the lambs had free access to forage (maize and bean harvest residues and alfalfa hay) and weaning concentrate.After this period, males were given free access to fattening concentrate and females to growing concentrate for 54d (Tab.1).The diets were adjusted according to the requirements of Nutrient… (1985).To evaluate the effect of ram breed and the cross of Dam with Dor ewes on carcass characteristics, at the end of fattening, three treatments were formed consisting of the following crosses: T1, Dam x KatDor (n=6); T2, Dam x BbPb (n=6), and T3, Dor x BbPb (n=4).Average weight was 33.6kg.The lambs were sacrificed and the hot carcass was weighed and refrigerated at 4ºC for 18h.After this period, the cold carcass was weighed, the Longisimuss dorsi area between the 12 th and 13 th rib was calculated, and dorsal fat thickness was measured on the 12 th rib, on the rump and at the base of the tail with a Vernier.Primal cut yield of the carcass (tail, leg, neck, loin, rib, foreshank, flank, hindshank, and skirt) and surplus fat.
The percentage of single and multiple births was analyzed with the CATMOD procedure considering the principal effects breed, age, and their interaction.Weight at birth of the lambs was analyzed with the MIXED procedure, which included the fixed effects of the ram breed, ewe race group, type of lambing, sex and their possible interactions, as well as the random effects of the sire within the sire breed and the dam within the dam breed.The statistical procedure for weaning weight was similar to that used in the analysis of weight at birth, but the fixed effect type of lambing was changed for type of weaning.Due to the differences in postweaning feeding, the analysis of post-weaning weight was done in male and female lambs separately.The model included the ram race, the mother's race group, type of weaning and their possible interactions, as well as the random effects of the sire within the sire breed and the dam within the dam breed as fixed effects.
Carcass assessment was done with the GLM procedure, considering the cross as fixed effect and weight at sacrifice as co-variable (SAS, 2002).

RESULTS AND DISCUSSION
For groups Bb, Dor, Kat, and Pb, lambs born alive per ewe were 1.77, 1.27, 1.39 and 1.42, respectively.In Figure 1, it is observed that Bb has a larger percentage of multiple births than Dor (P<0.05).The average (1.55) number of live-born lambs in Pb in this study is similar to that reported by Macedo and Alvarado (2005), although it contrasts with 2.24 lambs born alive per ewe, with intensive feeding evaluated by these authors.Hinojosa et al. (2005) et al. (2005).These authors increased the number of lambs born to 1.26 and 1.47 by applying 300IU PMSG 24 h before withdrawing the sponge.These values are similar to those of Dor ewes in our study, although the ewes were not synchronized with hormone treatments that might have changed their reproductive response.Ewes that were younger than four years old had 1.26 lambs born alive, while ewes four years or older had 1.55 lambs; that is, the percentage of multiple lambings was higher (P<0.05) for the older ewes (Fig. 2).A lower number of lambs per parturition has also been observed in Suffolk and Targhee ewes less than two years old (Bunge et al., 1993).Moreover, Burke (2005) reported that lamb litter weight increases with age of Kat, Dor and St. Croix ewes; this may be due to the larger number of multiple lambings of ewes older than 1 year, relative to younger ewes.Among the female lambs there was no difference due to ram breed or racial group of the mother (Fig. 3).Among the single male lambs born to BbPb mothers, it was found that the offspring of Dor rams (3.88kg) were heavier (P<0.05) at birth than those of Dam rams (2.87kg); this is because Dor rams are heavier than Dam rams.Single birth BbPb male lambs were 383g lighter (P<0.04)than KatDor male lambs, while twin lambs were 660g lighter.This may have been due to the heavier weight of the KatDor ewes since Bb and Pb are smaller breeds (Arredondo-Ruiz et al., 2013).López-Carlos et al. (2010) report that pure bred Dor and Kat ewes have heavier lambs than Bb and Pb.Hinojosa et al. (2005) report birth weights of 2.93kg for Dor x Pb, similar to female and male Dor x BbPb offspring from multiple lambings, but lower than lambs from single births.All of the birth weights of Dor ram offspring are lower than the weights reported by Snowder and Duckett (2003) for offspring of Dor rams crossed with Columbia ewes.This may be due to the larger size of Columbia ewes.For pure Dor, birth weights of 3.1kg have been reported (Burke and Apple, 2007).Birth weights of pure Katahdin are reported at 3.6kg (Burke et al., 2003) and 3.4kg (Burke and Apple, 2007).Weaning weight of female lambs from KatDor ewes crossed with Dor rams (21.18kg) was higher (P<0.01)than those from KatDor ewes mated with Dam rams (15.6kg).There were no differences (P>0.05) in weaning weight of male lambs by effect of ram or ewe breed.Hinojosa et al. (2005) registered an average weaning weight (83d old) of 12.44kg for female and male Dor x Pb lambs raised in tropical conditions.This weight is lower than that of Dor ram offspring weaned at 65d reported in our study.The better productive response of the lambs of this research may have been due to the balanced diet that covered their nutritional requirements.
Lambs from South Africa (21.7kg) have better weaning weights than those raised in the US (19.4kg) (Notter et al., 2004); these averages are higher than the live weight of Dor ram offspring when they are from multiple weaning but are similar to the average of single weaning offspring of our study.Weaning weights at 58-66 d of 19.2kg have been reported for purebred Katahdin lambs (Burke et al., 2003).Post-weaning daily weight gain of male lambs was not affected (P<0.05) by ram breed, group of the mother, or weaning type (Tab.3).Female lambs of Dor rams had a post-weaning daily weight gain 16.6 % higher (P<0.05)than female lambs of Dam Rams (Tab.2).These postweaning gains are similar to those reported for the offspring of Dor (239g), Columbia (239g), and Suffolk (259g) ram mated with Columbia ewes (Snowder and Duckett, 2003).However, the post-weaning gain obtained in our study for females and males is higher than that reported by Wildeus et al. (2005), who achieved daily weight gains of 73g for female and 109g for male Bb and Kat fed forage and concentrate with 15.7% CP administered at 1.5% live weight.The higher post-weaning weight gain of Dor ram offspring, compared with Dam offspring, is possibly because Dor ewe is a meat breed that can reach a weight of 70.2kg or more depending on feed management (Burke, 2005).

CONCLUSION
Blackbelly ewes are more prolific than Dorper ewes.Katahdin-Dorper ewes gave birth to heavier male lambs than Blackbelly-Pelibuey ewes.At weaning, female lambs from Katahdin-Dorper ewes crossed with Dorper rams were heavier than lambs from ewes of the same group crossed with Damara rams.In fattening of the male lambs, no effect of the ram or ewe breed on daily weight gain was found, although in the case of the females, Dor ram offspring achieved higher weight gain.In terms of carcass dressing, subcutaneous fat and important primal cuts characteristics, there was no effect of crossing Damara and Dorper rams with Blackbelly-Pelibuey ewes or of the Damara x Dorper cross.

Figure 2 .
Figure 2. Percentage of single and multiple lambings of ewes less than four years old and ewes older than four years old.a, b Different letters indicate significant difference between age groups (P<0.05).

Table 1 .
Nutrients for sheep diets at five physiological stages analyzed the records of grazing ewes in the humid tropics and found that Bb is more prolific than Pb or crosses with Dor and Kat in different years.In this study Bb had a higher percentage of multiple births, coinciding with findings of López-Carlos et al.

Table 2 .
Post-weaning daily weight gain (g d -1 ) for male and female lambs by ram breed, ewe race group and weaning type at 69d post-weaning