Effects of flushing with two energy levels on goat reproductive performance

The objective of this study was to evaluate the effects of supplementation with two concentrate levels (CL) on body condition score (BCS), and body weight (BW) of breeding goats, number of kids born, birth and weaning weight, and rate of weight gain of the offspring. Treatments were a high CL (600g/d of grain mix; 1.8 Mcal ME) and a low CL (300g/d; 0.9 Mcal ME) in a completely randomized design. Six nannies (BW=38.5kg, BCS=2.8) were randomly assigned to each treatment. The goats grazed native grass pastures. Flushing started 21-d prior to introduction of the buck and continued for 42-d. Thereafter, all nannies were fed a low CL until parturition. Nannies were weighed at the start of flushing, and at 9 and 96 days after introduction of the buck. BCS was estimated monthly. The kids were weighed at birth and weekly until weaning (45 days).

There were no effects of CL (P>0.05) on BW, BCS, and kid numbers, but, kid birth weight was lower with the high compared to the low CL (2.5 vs. 3.3kg). This was a result of more twinning with the high CL. There was also no effect (p>0.05) of CL on weaning weight (8.2 vs. 7.8 kg) and weekly rate of weight gain (860 vs. 727g) with the high and low CL, respectively.

In conclusion, CL greater than 300g/d prior to and during the mating season did not improve reproductive performance in meat goats. However, similar studies conducted in nannies with lower initial BCS than those of the present experiment or with more animals per treatment might show a benefit of the higher supplementation level.

Key words: concentrates, condition score, forages, grazing, mating season, reproduction

Introduction

Productivity of goats is fostered by the efficient utilization of nutrients which is possible with an adequate supply of energy. Energy requirements are affected by age, body size, physiological state, environmental factors, hair growth, muscular activity, and relationships with other nutrients. Weather conditions such as temperature, humidity, sunshine, and wind velocity may increase or decrease energy needs depending upon the region. Stress of any kind may increase energy requirements (NRC 1981).

Although goats tolerate high temperatures and humidity of the tropics, they do experience reproductive problems associated with nutritional deficiencies, particularly from low quality forages. In a grazing situation, animals having the highest nutritional requirements should have access to lush, leafy forage or high quality browse. Additionally, goats should be supplemented with a concentrate feed when the forage that they are grazing does not contain the necessary nutrients to cover their nutritional requirements (Luginbuhl and Poore 1998).

Deposition of lipids is the main form of energy storage in goats and is important in determining body condition score (BCS). When goat nannies present poor BCS, they often have low conception rates, low twinning rates and kids with low birth and weaning weights (Cissé et al 1992; Luginbuhl 1998). Goats lose body condition with the progressive deterioration of pasture in the dry season. This condition can be improved with a sufficient level of concentrate supplementation.

A common practice in females of different species is to prepare them for the breeding season by flushing. In goats, this practice consists of an increase in the level of energy offered from prior to introduction of the buck to until approximately 21 days thereafter (Luginbuhl and Poore 1998). Several studies in small ruminants have shown that with flushing ovulation and fetal implantation in the uterus are improved (Kusina et al 2001; Acurero 2000; Martínez et al 1986).

In this study of meat goats grazing native pastures, the objective was to evaluate the effect of flushing with two energy levels on maternal BCS and body weight (BW), kids borne and their birth and weaning weight, and rate of weight gain.

Materials and methods

Twelve adult goats from 1.5 to 3 years old, with average BW 38.5 ± 6.3 kg were randomly assigned in two groups, which were balanced according to BW and age. The treatments were a high CL (600g/d of grain mixture; 1.8 Mcal/kg ME) and a low CL (300g/d; 0.9 Mcal/kg ME). This supplementation started 21-d prior to introduction of the buck and continued for 42-d during the breeding period (63-d total). Thereafter, all nannies were fed a low CL until parturition. All nannies grazed native pastures (Dichanthium annulatum, Heteropogun contortus, Cynodon dactylon) during the day and were housed in a shelter at night. They also had free access to water.

Nannies were weighed bi-monthly and their BCS estimated monthly on a rating scale from 1 to 5 (Spahr 2004). For determining the effect of dietary energy level on ovarian activity, number of kids born per reproductive female was used. Kids were weighed at birth and every 7 days thereafter until weaning (45-d) and weight gain (g/week) was calculated.

The chemical composition of the basal diet and grain mix was determined in external laboratories (Table 1).

Table 1. Chemical composition (dry basis) of the basal diet and concentrate supplement
Component	Pasture forage	Grain mix
¹DM, %	93.1	89.4
¹CP, %	7.98	15.8
¹NDF, %	70.2	27.5
¹ADF, %	42.9	11.4
¹Ca, %	0.31	1.15
¹P, %	0.19	0.83
²GE, Mcal/Kg DM	3.99	3.94
³ME, Mcal/Kg DM	1.8	3.0
¹Laboratory Dairy One ²Thermodynamic laboratory, Universidad Nacional de Colombia ³ Estimated for concentrate (GE0.75) and for forage (GE0.44).

The metabolizable energy (ME) of pasture forage was estimated at 44% of gross energy (GE). This figure was arrived at assuming a digestibility value of 55%, as reported by Vicente-Chandler et al (1974) for gramineous forages in Puerto Rico, and typical losses of 4% in urine and 7% in combustible gases (Van Soest 1994). The grain mix was a commercial product of unknown formula. It was assumed to have a ME value equal to 75% of GE based on its chemical composition and probable approximate formula in terms of ingredients used by the local feed industry.

The data were analyzed using a completely randomized design with the GLM procedure of the statistical program SAS/STAT 9.1 (SAS 2004). Dependent variables analyzed were: BCS and BW of nannies, number of kids born, birth and weaning weight, and rate of weight gain of the offspring. The model used was Yij = µ + aj + Eij, where, aj was the effect of the treatment (CL).

Results

Nannies

The chemical composition of the pasture forage available to the nannies, shown in Table 1, is typical of local gramineous swards.

The BCS increased in all nannies over the period of flushing (Figure 1), but there were no effects of CL (P>0.05).

Mean BCS values were 3.02 and 2.97 for high CL and low CL respectively. The initial BCS of the two groups was not far below 3, and it is possible that with a lower initial BCS the CL might have had significant effects. With the flushing, most of the goats of both groups had a BCS above 3 upon beginning gestation. After giving birth the BCS of the nannies in both groups decreased, but the drop was more notable in those that received low CL than high CL.

Numerically the mean BW of the nannies supplemented with high CL exceeded that of the low CL group (42.9 kg and 40.8 kg respectively), but not significantly so (p>0.05). Figure 2 shows the increase in body weight of the two groups of nannies during flushing (-21 to 42 days) and gestation.

There was no statistically significant difference between treatments in kidding number. The means for the high and low CL groups were 1.6 and 1.3 kids per goat, respectively (Table 2).

Table 2. Reproductive performance of nannies supplemented High (600g/d; 1.8Mcal ME) and Low (300g/d; 0.9Mcal ME) concentrate levels
	High	Low
Number goats	5	6
Number birth kids	8	8
Number weaned kids	6	8
Kids birth per goat	1.6	1.3
Birth weight, kg	2.49	3.29
Weaning weight, kg	8.17	7.78
Twinning rate, %	60	33.3
Number females	3	4
Number males	5	4

These values represent a twinning rate of 60% (3/5 nannies) and 33.3% (2/6 nannies) for high and low CL, respectively.

Kids

Birth weight of kids was significantly lower (p=0.031) in those nannies supplemented with high CL compared to low CL (Figure 3).

The respective means were 2.5 and 3.3 kg kid^-1. This result was affected by more frequent twinning under the CL treatment. Although the birth weight was different, the weaning weight and weight gain were unaffected by CL (p>0.05). Figure 3 shows that the BW of kids of both treatments was similar from 14-d until weaning at 45-d. Mean weaning weights and weekly weight gains were 8.17 kg and 7.78 kg and 860 and 727g for high and low CL respectively.

Discussion

Flushing improved the BCS in all nannies, but there were no significant differences between supplementation CL. The mean initial BCS of all goats was 2.8, and in both groups it increased to values above 3 in the breeding and gestation seasons. Spahr (2004) and Villaquirán et al (2004) recommend a BCS of 3.0 to 3.5 as optimal for goats in the breeding season. According to Luginbuhl and Poore (1998), animals with extremely good body condition tend not to respond to flushing. Dapoza et al (1995) in a study in sheep to evaluate the effect of BCS on ovarian activity, recommend flushing for females with BCS below 2.5.

The trend in BW evidenced a pattern similar to that of BCS during the experiment. It increased with the flushing but there were no significant differences between CL. However, as shown in Figure 2, BW was numerically higher with high than with low CL during nearly the entire experiment, the mean difference being 2.1 Kg.

Contradictory results have been reported regarding the BW response to energy supplementation of reproductive females. Sahluf et al (1995) evaluated three dietary ME concentrations (1.80, 2.16 and 2.53 Mcal/kg DM) prepartum and found that the weight gain was unaffected by energy level. Lu and Potchoiba (1990) also evaluated three dietary energy concentrations (2.46, 2.77 and 3.05 Mcal ME/kg) and observed no differences in weight gain in a period of 16 weeks. They attributed this result to the inverse relationship between dry matter intake and dietary energy density. However, Mahgoub et al (2005) evaluated three dietary ME concentrations of 2.1, 2.38 y 2.68 Mcal/kg DM and found a positive effect of increased energy supplementation on BW of Omani Batina and Dhofari goats.

There was no significant difference between treatments in number of kids born per nannie. However, the numerical difference in this case is biologically important. In the low CL treatment two of six reproductive females had twins, while with high CL it was three of five. These data show a tendency to more frequent twinning with high level supplementation (1.8 Mcal ME /day). This difference affected the birth weight of the kids, which was significantly lower with high CL. Naturally twins tend to have lower individual birth weight. In spite of a lower mean birth weight, the kids of the high CL treatment responded during the rest of the experiment in the same manner as those of low CL (Figure 3), and there were no significant differences in weight gain and weaning weight. In weaning weight a numerical advantage of 400g was observed with high CL.

Kusina et al (2001) evaluated three levels of energy intake of 0.27 (Low), 0.53 (Medium) and 1.06 (High) MJ ME Kg^-1 W^0.75 in forty-five multiparous Mashona goat does, starting 60 days pre-synchronization of estrus. They found that the twinning rate was significantly lower (p<0.05) for the low energy treatment than for the others and recommend the medium level to achieve satisfactory results in terms of estrus, conception rate, fecundity and twining rates. Both said results and those of the present study, in which the number of kids per doe was greater with high CL indicate that flushing can improve the ovulation rate. According to Landau et al (1997) long-term (>3 weeks) effects of over-nutrition on ovulation rate are mediated through improved BCS, whereas short-term effects are achieved through provision of nutrients that modify the hormonal environment, with no alteration of BCS. Walkden-Brown and Bocquier (2000) suggest that energy availability has a key influence on reproductive performance, due to the sensitivity of the reproductive axis to the adequacy of nutrition and stores of metabolic reserves. Blood metabolites such as glucose, NEFA and B-hydroxy-butyrate and certain metabolic hormones (insulin, somatrophin, thyroxine, cortisol, prolactin and IGF-1) are considered to be limiting factors and may serve as a signal either at the gonadal or at the central level of regulation of reproduction (Chilliard et al 1998).

The concentrate used in this study was estimated to have 3.0Mcal ME/Kg and to supply 1.8 and 0.9 Mcal ME/d with high and low CL respectively. The pasture forage was estimated to contain 1.8 Mcal ME/Kg. From this assumption, the dietary energy intake was calculated as 3.8 and 2.9 Mcal/d for the high and low CL treatments. Comparing these energy intakes with the theoretical requirements of adult goats (2.82 Mcal ME; NRC 1981), it seems that even the lower CL treatment covered the requirement while the high CL exceeded it by 26%. Future studies using energy intake levels lower than the animal’s requirement, might demonstrate differences in favor of the high supplementation rate (1.8 Mcal ME/d).

Goonewardene et al (1997) conducted a study with twenty two Alpine and twenty Saanen goat does fed two pre-service diets. The diets supplied 3.2 and 3.5 Mcal DE/d corresponding to 10 and 20% more than the NRC (1981) maintenance requirements. The goats were fed these diets for 8 weeks, after which those of the low energy (3.2 Mcal DE/d) group were switched to the high energy treatment (3.5 Mcal DE/d). A week later, estrus was synchronized and the does were inseminated artificially. No effect of energy intake level was found on expression of estrus, conception rate and twinning rate. These results demonstrate the difficulty of finding differences between energy levels all of which surpass the minimum requirements, as happened in the present study.

The small number of goats used in this study could have impeded finding significant differences in the variables: maternal BW, kids per doe and weaning weight, so that only tendencies were observed. Additional studies including more animals are needed. Although investigation into nutritional requirements and the relationship between nutrition and reproductive performance of goats has increase in recent years, more information is necessary because the results are contradictory. More information is available on the interaction of nutrition and reproduction in cattle and sheep. Further studies, including an analysis of economical profitability are necessary to define the optimal levels of energy to use in flushing under different productive conditions, thus to give the best recommendations to goat producers.

Conclusions

Acknowledgment

This research was supported by USDA Tropical and Subtropical Agricultural Research (TSTAR), (Project No. TSTAR 105 of the Agricultural Experiment Station, University of Puerto Rico, Mayaguez).

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Effects of flushing with two energy levels on goat reproductive performance

A Acero-Camelo, E Valencia*, A Rodríguez and P F Randel

Animal Industry Department. University of Puerto Rico, PO Box 9030 Mayagüez, P.R.00681

*Agronomy and Soil Sciences Department. University of Puerto Rico, Mayagüez,P.R.

rac23585@uprm.edu

Abstract