Non-genetic factors affecting pre-weaning growth and morphometric traits in Assam Hill goat

Aim: This study aimed to determine the genetic and non-genetic factors affecting pre-weaning body weight (BW) and morphometry in Assam Hill goat along with the genetic parameters. Materials and Methods: The detailed information in respect of BW and body measurements of 960 animals at birth and 3 months of age belonging to three different populations of Assam Hill goat maintained at field units, namely, Batabari, Nahira, and Tetelia under “All India Coordinated Research Project on Goat Improvement” were utilized in the present study. The data were analyzed using least squares technique. Results: The least squares means for BW, height at withers (HW), heart girth (HG), and body length (BL) were 1.166±0.008 kg, 26.198±0.070 cm, 26.695±0.096 cm, and 29.482±0.119 cm at birth and 4.590±0.083 kg, 36.850±0.105 cm, 40.741±0.115 cm, and 39.703±0.108 cm at 3 months of age, respectively. Location had a significant effect on BW, HW, and BL at both birth and 3 months and on HG at 3 months of age. Season of birth exerted significant effect only on BL at birth, whereas the significant effect of sex was observed on HG and BL at 3 months of age. The heritability estimates for BW and body measurements were moderate indicating the scope of selection. The phenotypic and genetic correlations among BWs and body measurements at birth and 3 months of age were positive in direction and high in magnitude. Conclusion: On the basis of the present findings, it could be concluded that the weaning weight of kids can be considered for the selection of parent stock to increase productivity and eventually the economic efficiency. Further, animals with higher body measurements at initial phases of growth will perform better with respect to even BW at later stages of growth.


Introduction
Goat substantially contributes to the rural economy and provides a livelihood to the poor sections of the society. India possesses the second largest goat population in the world with 135.17 million goats (26.40% of the country's total livestock) which corresponds to 15.68% of total goat population in the world [1]. The goat population of Assam is 6.169 million, contributing 4.56% of total goat population of India [1]. The Assam Hill goat is a newly registered breed distributed throughout the state of Assam possessing good quality meat and high adaptability characteristics to local high humid agro-climatic condition. Almost the entire population of Northeastern region of India is non-vegetarian and chevon is the meat of choice having no religious taboo. The chevon production in Assam in the year 2012-2013 was 11,000 tonnes which were 20% of the total meat produced in the state [1]. The gap between demand and production of meat could be bridged by augmenting the growth performance and reproductive efficiency of the animals.
Birth weight is an important parameter in meat-producing animals due to its strong correlation with growth rate and adult size as well as with the viability of newborn animals, while weaning weight has a high relative economic importance to the farmers [2]. Evaluation of early growth and morphometric traits indicates the growth trends which enable more accurate assessment of growth potentials; better understanding of the impact of genetic and environmental factors on growth; more accurate prediction of mature growth and linear body values before attainment of maturity; and early selection, reduction of generation interval, and rapid genetic progress [3]. In meat-producing animals, external body measurements could be a reliable indicator of its future performance with respect to live body weights (BWs), if and only if a correla tion has been identified among these traits of interest [4]. To formulate efficient breeding plans and selection strategies, knowledge of genetic parameters (heritability) among various traits is essential [5,6]. This study aimed to determine the genetic and non-genetic factors affecting pre-weaning BWs and morphometry in Assam Hill goat along with the genetic parameters.

Location and data collection
The animals used in this study were reared by the farmers belonging to the field units under "All India Coordinated Research Project on Goat Improvement," Goat Research Station, Assam Agricultural University, Burnihat. The location lies between 90.48° and 92.22° (East) longitude and 20.09° and 26.95° (North) latitude. The data pertaining to 960 animals were utilized in the present investigation. Measurements of four morphological characters, namely, BW, height at withers (HW), heart girth (HG), and body length (BL) were recorded at birth and 3 months of age according to measurement regions [7]. Measuring tapes were used to record the length and HG in centimeter, while the heights were measured using graduated stick. The BWs were measured using spring balance of 50 kg capacity in the morning hours. The birth weights of the kids were recorded within 12 h of birth. The data were classified into three locations, namely, Batabari (L 1 ), Nahira (L 2 ), and Tetelia (L 3 ); four seasons of birth, namely, pre-monsoon, i.e., March-May (S 1 ), monsoon i.e., June-September (S 2 ), post-monsoon, i.e., November-December (S 3 ), and winter, i.e., December-February (S 4 ); and two sexes as male and female.

Management practices
The goat sheds were made of locally available materials, i.e., bamboo, wood, thatches, etc. The slotted floors of the houses were raised by about 3 ft. The walls of the shed were made of bamboo and covered up to three-fourth of the total height of the wall and rest of the portions were kept open for ventilation. The animals were kept under semi-intensive management system. Selective breeding was practiced where the breeding does were mated with superior bucks supplied under the project. All the male kids except those kept for breeding purpose were castrated before 3 months of age. The animals were immunized regularly against enterotoxemia, peste des petits ruminants, and goat pox. Regular deworming was practiced in all the field units under study.

Statistical methods
The data were analyzed using least squares means (LSM) as described by Harvey [8]. The statistical model used to analyze the data was Y ijko = µ+L i +M j +S k +e ijko , where Y ijko is the value of the o th animal in the (ijk) th subclass, µ is the overall population mean, L i is the be justified by proper postnatal care and management by the farmers of Tetelia unit along with availability of mother's milk to the unweaned kids.

Effect of season of birth
Non-significant effect of season of birth was observed on both the traits (Table-2), which is in agreement with the observations of Faruque et al. [14] in Black Bengal goats for birth weight and Bedhane et al. [15] in Arsi-Bale goats for weaning weight. However, a significant effect of season of birth on both the traits was reported by Mahal et al. [16] in Black Bengal goats.

Effect of sex
Analyses of variance revealed that birth and weaning weight were not significantly affected by sex of kids though the weights of male kids were higher than the females (Table-2). Similar observations were obtained by Mia et al. [10] in Black Bengal goats. However, a significant effect of sex of kid was reported by Bedhane et al. [15] in Arsi-Bale goats for both the traits. The increase in BW of male goats might be attributed to the early activation of male gonads than the females. Male sex hormone testosterone responsible for the anabolic effect could have caused the faster growth in male animals.

HW, HG, and BL
The overall LSM±SE for HW, HG, and BL were 26.198±0.070 cm, 26.695±0.096 cm, and 29.482±0.119 cm at birth and 36.850±0.105 cm, 40.741±0.115 cm, and 39.703±0.108 cm at 3 months of age, respectively (Table-1). These findings are in accordance with the findings of Pan et al. [17] in Black Bengal goats. However, much higher values were recorded in Sirohi goats for all the traits by Dudhe et al. [18]. effect of i th location (i = 1, 2, 3), M j is the effect of j th season of birth (j = 1, 2, 3, 4), S k is the effect of the sex of the kid (k = 1, 2), and e ijko is the random error associated with Y ijko assumed to be NID (0, σ 2 e ). Duncan's multiple range test (DMRT) was done to make pairwise comparison among the means wherever significant differences exist.
The estimates of heritability (h 2 ), phenotypic (r P ), and genetic (r G ) correlations were calculated from the sire component of variance and covariance. The statistical model used to estimate the genetic parameters was Y ij = µ+S i +e ij , where Y ij is the observed value of j th progeny on i th sire, µ is the overall population mean, S i is the effect of i th sire common to all its progeny (i = 1,2,3...), and e ij is the random error component assumed to be NID (0, σ 2 e ). Standard errors (SEs) of heritability, phenotypic, and genetic correlation were estimated using the standard statistical methods.

Results and Discussion
The estimates of LSM and SE for BW, HW, HG, and BL at birth and 3 months of age along with the results of DMRT are presented in Table-1, and least squares analyses of variance showing the effect of different factors on the traits are presented in Table-2.

BW
The overall LSM±SE for birth weight were found to be 1.166±0.008 kg in the present study (Table-1) which is in conformity with the finding of Otuma and Onu [9] in Nigerian crossbred goats; while, the reports of Mia et al. [10] in Black Bengal goat support the mean value for weaning weight in the present study which was found to be 4.590±0.083 kg (Table-1). However, the present finding is higher than the finding of Miah et al. [11] for birth weight and the finding of Singh and Singh [12] for weaning weight in Black Bengal goats. In contrast, Syahirah et al. [13] reported higher values for both the traits in Boer kids.

Effect of location
Location had a significant effect on both birth and weaning weight (Table-2 ). Kids born at Nahira unit exhibited higher birth weights as compared to Batabari and Tetelia unit. This might be due to better management practices adopted by the farmers of Nahira. Weaning weight of kids of Tetelia unit significantly differed from the kids of Batabari. This could

Effect of location, season of birth, and sex of kids on morphometric traits
Location affected HW and BL significantly at both the age groups, but HG at weaning age only (Table-2).
Non-significant effect of season of birth on HW and HG at both age groups was observed in the present investigation (Table-2). However, a significant effect on HG was observed by Dudhe et al. [18] in Sirohi goats. On the other hand, there was a significant effect of season of birth on BL at birth in the present investigation (Table-2). The mean BL was comparatively higher in goats born during post-monsoon season. The result is in accordance with the finding of Dudhe et al. [18] in Sirohi goats.
Although differences in HW at birth and weaning due to sex were not significant, the values of the LSM for male animals were higher than those for the females (Table-2). On the contrary, sex of kids exerted significant effects on HG and BL at weaning in the present study (Table-2) which is in the flow of the reports obtained by Dudhe et al. [18] in Sirohi goats. The values of HG were found to be higher in male goats than those of females. However, a non-significant effect was observed by Kharkar et al. [19] in Berari goats.

Genetic parameters
The estimates of genetic parameters, namely, heritability (h 2 ), phenotypic correlation (r P ), and genetic correlation (r G ) along with the SE among BWs and body measurements at birth and 3 months of age are presented in Tables-3 and 4.

Heritability
The heritability estimates for birth and weaning weight under study were moderate (Table-3), which are in the line of the estimates of Kenneth et al. [20] and Kuthu et al. [5] in meat goats of the USA and Teddy goats, respectively. Moderate estimates indicated the scope for improvement of the traits through selection. However, lower estimates of heritability were obtained by Faruque et al. [14] in Black Bengal goats for birth weight and Bedhane et al. [15] in Arsi-Bale goats for weaning weight. On the contrary, higher values than the present estimates were reported by Mia et al. [10] in Black Bengal goats for both the traits.
Similarly, moderate estimates of heritability were obtained for HW, HG, and BL at birth and weaning in the present study (Table-4) which also indicated scope of improvement by selection. However, Dudhe et al. [18] in Sirohi goats reported higher estimates of heritability for morphometric traits as compared to the present estimates.

Phenotypic and genetic correlation
The phenotypic and genetic correlations among pre-weaning BWs were found to be positive and high at both the age groups (Table-3). It has considerable significance in the selection program for BW since BW at one of these early ages is a good indication of BW at 12 months of age. These high correlations are of economic importance and suggest that the genetic factors are largely similar for these early and 12 months of age. These findings are in conformity with the findings of Mia et al. [10] in Black Bengal goats.
The phenotypic and genetic correlations among BWs and various body measurements were found to be positive and high at both the age groups (Table-4). This indicated that the linear body measurements could reliably play a predictive role for BW at any given age. BW appeared to be a function of these body measurements. This indicated the possibility of improving BW as a correlated response by exerting selection pressure on the body measurements. Dudhe et al. [18] in Sirohi goats reported positive and high phenotypic and genetic correlation among body measurements as obtained in the present study.

Conclusion
Weaning weight of kids can be considered for the selection of parent stock to increase productivity and eventually the economic efficiency. These results, therefore, provide an important perspective on the selection objectives of Assam Hill goats by considering different environmental factors. Since BW Table-4: Estimates of heritability (h 2 ), phenotypic (r P ), and genetic (r G ) correlation between body weight and body measurements at birth and 3 months of age. N.B. The elements of the diagonal are the estimates of heritability, above the diagonal is the phenotypic correlations, and below the diagonal is the genetic correlations. BW=Body weight, HW=Height at withers, HG=Heart girth, BL=Body length and body measurements are important parameters to describe growth, so selective breeding of Assam Hill goat based on these parameters needs to be given more emphasis for greater productivity.