Genotype by environment interaction: a case study of productive and reproductive performance of Yellow local and F1 (Red Sindhi x Yellow local) cattle in two production zones in Quang Ngai, Vietnam

L D Phung

Department of Animal Sciences, Hue University of Agriculture and Forestry, 102 Phung Hung Street, Hue city, Vietnam
Phung.ledinh@gmail.com

Abstract

This research is aimed at investigating the effects of a crossbreeding program on productive and reproductive traits of Yellow local and F₁ crossbred (Red Sindhi x Yellow local) cattle in the lowland and mountainous zones in Quang Ngai province, Vietnam. The studied traits were: chest girth development, age at first calving, gestation length, time from calving to pregnancy and calving interval of the crossbred and the Yellow cattle.  

In the mountainous zone, the Yellow local cattle had a higher chest girth growth/month and a better reproductive performance. Yellow local cattle had an earlier age at first calving, a shorter time from calving to pregnancy and calving interval than those for the crossbred cattle. In the lowland zone, the crossbred cattle had a higher chest girth growth, but were reproductively not superior to the Yellow local cattle.  

The productive and reproductive results suggest that genotype by environment interactions occur on the productive and reproductive traits of cattle. The propagation and extrapolation of the use of crossbred cattle should be carefully considered in line with feeding practice and management. 

Key Words: crossbred, productive traits, reproductive traits, Yellow cattle

Interacción Genotipo x Medio Ambiente: estudio de caso del desempeño productivo y reproductivo de ganado Amarillo local y F1 (Red Sindhi x Amarillo local) en dos zonas productivas de Quang Ngai, Vietnam

Resumen

Esta investigación tenia como objeto el estudiar los efectos de un programa de cruza en los rasgos productivos y reproductivos de ganado Amarillo local y F1 (ed Sindhi x Amarillo local) en las zonas bajas y montañosas de la provincia de Quang Ngai, Vietnam. Los rasgos estudiados fueron: desarrollo de la circunferencia del pecho, edad al primer parto, duración de la gestación intervalo parto-preñez e intervalo entre partos en el ganado Amarillo y el cruzado.

En la zona montañosa el ganado Amarillo local tuvo un mayor crecimiento mensual de la circunferencia del pecho y un mejor desempeño reproductivo. En el ganado Amarillo local la edad al primer parto fue menor, el periodo del parto a la preñez fue mas corto al igual que el intervalo entre partos, comparado con los cruzados. En las zonas bajas, el ganado cruzado tuvo un mayor desarrollo de la circunferencia del pecho, pero no presentaron diferencia reproductiva respecto al ganado Amarillo local.

Los resultados productivos y reproductivos sugieren que la interacción genotipo x medio ambiente se presentan en los rasgos productivos y reproductivos del ganado. La divulgación y extrapolación del uso de ganado cruzado debe considerarse cuidadosamente junto con las prácticas de alimentación y manejo.

Palabras clave: cruces, rasgos productivos, rasgos reproductivos, ganado Amarillo

Introduction

For over a decade Red Sindhi (Zebu) crossbreeds (Red Sindhi x Yellow local) have been introduced in mixed farming systems in all agro-ecological zones of Quang Ngai and other provinces in Vietnam. The cattle crossbreeding program (VN2561), funded by world bank has been considered a major livestock development activity of Quang Ngai Provincial Department of Agricultural Extension and Rural Development. However, up to now, there has not been any detailed and quantitative information on productive and reproductive performance of the crossbred (C) and the Yellow local (Y) cattle at different zones.  

Effects of the crossbreeding program on productive and reproductive performance of the crossbred cattle depend on the conditions of the production systems. A genotype by environment interaction (GxE) is expected, resulting in one most favourable breed for a specific zone (Holmes et al 1992; Vercoe and Frish 1992; Richard 1997). The knowledge on GxE  is important for policy makers, for animal breeders and especially for farmers for selecting the appropriate cattle breed for a specific zone. Therefore, the objective for this investigation was to quantify the effects of the crossbreeding program on the productive and reproductive traits of crossbred and Yellow local cattle in lowland and mountainous zones in Quangngai province.  

 

Materials and methods

Research location

Quang Ngai province is located in the south central coast of Vietnam with an area of about 58,497 km² and population size around 1.2 million people. Climate is tropical monsoon. The research was conducted at 15 villages of three communes of Bato, Badong, and Bacung, representing the mountainous zone (M) and 12 villages of two communes of Nghiadung and Hanhthinh, representing the lowland zone (L). The M zone has an area of about 391,192 hectares, occupying nearly 2/3 of the total area of the province. The L zone is about 150,678 ha with a more ecological diversification than the M zone.  

Cattle management and feeding practices 

The L and M zones differed in the use of land for cattle production. In the M zone cattle had free access to natural pasture on the hills and forest edges. In the L zone cattle are, however, provided with cut and carried grasses from home garden or rice field. Land resource shaped the cattle management and feeding practices of cattle production in both zones. Grazing was the main feeding practice of cattle in the M zone, while it was stall fed in the L zone.  Cattle in the M zone had a higher number of grazing days per year and number of grazing hours per day than cattle in the L zone.  In the M zone the crossbred (C) and Yellow (Y) cattle did not differ in grazing days per year and grazing hours per day. This is, however, not the case for the C and Y cattle in the L zone, where the C cattle had fewer grazing days and shorter grazing hours.  The difference also occurred in the use of external inputs, especially concentrates. The C cattle in the M zone were provided fewer concentrates than cattle in the L zone. The C cattle in the L zone consumed more concentrates than the Y cattle. In the M zone, however, this is not the case. 

There were vet networks in the researched area, where veterinarians were responsible for AI and livestock disease prevention and treatment. The network was run rather well in the L zone, but this was not the case in the M zone, because of difficult topography, weak infrastructure, a small number of vets per district, and the limited skills of vets. Moreover, the commercialisation in cattle production in the L zone was higher than in the M zone. As a result, the L households were more concerned with cattle health and more willing to invest in cattle production than the M households. 

Briefly, the feeding practices and management showed that the level of investment for cattle production in the L zone was higher than in the M zone. In the L zone, the C cattle were kept more intensively than the Y cattle; but in the M zone there were no differences between the C and Y cattle in terms of feeding practices and management. 

Data collection and variables 

Chest girth (CG-cm) was used to evaluate the performance of cattle in terms of beef production. CGs were measured by using a string ruler on F₁ (Red Sindhi x Local yellow) and Local Yellow  cattle at different ages (3, 4, 5, 8, 12, 14, 17 and 22 months). The measurement was on 83 and 76 Y cattle and 148 and 93 C cattle for L and M zones, respectively. 

Age at first calving (mo), calving interval (mo), gestation length (d) and time from calving to pregnancy (mo) was used to evaluate the performance of cattle in terms of reproductive viability. Questionnaires were used to interview the cattle rearing householders on reproductive traits of F₁ breed (Red Sindhi x Yellow local) crossbreeding cows mated with Red Sindhi bulls to produce F₂ ¾ Red Sindhi and local cows mated with Red Sindhi bulls to produce F₁ ½ Red Sindhi. In the L zone, the sample size was 91 and 193, respectively for C and Y cows. In the M zone, the sample size was 52 and 118, respectively for C and Y cows. 

Age at first calving, calving interval, time from calving to pregnancy, and gestation length were estimated by averaging the data from all animals surveyed. The calculation of the criteria was not based on herd dynamics, because there were no recording systems in the research area (also in the other provinces of Vietnam) and our survey was conducted at that point of time. Therefore, herd fluctuations, which are necessary for calculating heard dynamic criteria, were unavailable to quantify. 

Statistical model 

The General Linear Model-Multivariate procedure from the GenStat (2004) was used to analyse the data. Effects of zone and breed genotype on productive and reproductive traits of cattle were analysed by model [1]

Y_ijk = m +a_i +b_j  + g_ij + e_ijk                  [1]

Y_ijk  is the measurement of animal k within zone i and breed j,

m is  the overall mean,

a_i is the effect of zone i (i=1 for L zone; i=2 for M zone),

b_j is the effect of cattle breed j (j=1 for C cattle; j=2 for Y cattle),

g_ij is the interaction between zone i and breed j and

e_ijk is the random term for animal k within zone i and breed j.

If the interaction between zone and breed was significant (p<0.05), the model [1] was changed into a nested model:

Y_ijk = m +a_i +b_j(a_i) + e_ijk                             [2]

where b_j(a_i) is the effect of cattle breed j within zone i and other parameters and variables are the same as in [1].

A nested model can analyse the effect of breed within each zone: b(a₁); -b(a₁); b(a₂);  -b(a₂). In other words, a nested model can show GxE interaction.

The parameters in model [1] and [2] were estimated by the method of Angela and Daniel (1999) using the sum restriction  and

so that "m" expresses the overall mean.

If the interaction between zone i and breed j was not significant (P>0.05) the model [1] was changed into a model without interaction: Procedures for the estimation of parameters are in table 1. 

Table 1.  Parameter calculation and interpretation of the effects of zone and cattle breed for model with and without interaction
Effects	Parameters		Calculated as
	No interaction	Interaction
L zone	a	a
M zone	-a	-a
C cattle in the L zone		b(a1)
Y cattle in the L zone		-b(a1)
C cattle in the M zone		b(a2)
Y cattle in the M zone		-b(a2)
C cattle	b
Y cattle	-b

Results

Productive performance of Y and C cattle

There were no recording systems of CG or body weight (BW) development of cattle, not even for crossbred cattle belonging to the crossbreeding program in the research area. Therefore, the data of CG and BW cattle at particular stages of age were unavailable. In addition, BW was also impossible to measure directly, because electronic scales were not available in the research area. Therefore we used CG measured with a ruler to evaluate the effects of the crossbreeding program on the growth of cattle.

Overall means, degrees of freedom of error, parameters and tests of significance and residual standard deviations for chest girth of the C and Y cattle (table 2) are given at 3, 4, 5, 8, 12, 17 and 22 months of age. It can be seen from the table that the values of the parameters a and b are highly significant, which means that zone and breed had a significant effect on chest girths (CG) of cattle from 3 to 22 months of age.

The effects of zone were rather constant (about 4 cm) over the whole period of 3 to 22 months of age. The effects of breed were also rather constant (about 5.9 cm) over the period 3 to 12 months of age. In the remaining period (17 to 22 months), the effects of breed were different per zone (about 9 cm in the L zone vs. 3.5 cm in the M zone), which means that GxE interaction did occur on CG of cattle at this age. The effect of breed was stronger than that of zone, which is explained by the magnitudes of the parameter b. Linear function was used to describe the average CG value.

CG_t = CG₀ + kt + error                   [4]

CG_t is CG at time t (mo), CG₀ is CG at starting time, k is the slope (cm/mo) of CG per month and e is the error term. 

Estimates for CG₀ and k are in table 3. C cattle in the L and M zones had higher starting values than the Y cattle; 109.7 vs. 99.5 and 96.7 vs. 90.7 cm respectively. K for the C cattle in the L zone was 2.34 cm, which is 0.18 cm higher than that of the Y cattle at the same zone. For the C cattle at the M zone k was estimated 0.05 cm lower than that for the Y cattle. The interesting results point out that the C cattle had the highest growth in the L zone; but in the M zone it was the Y cattle. The results once again show that  the GxE interaction had effects on the growth in term of CG of cattle from 3 to 22 months of age.

Effects of zone and genotype on reproductive performance of C and Y cattle

Age at first calving (AFC), time till pregnant again (TPA), and calving intervals (CI) are important traits to evaluate the reproductive performance of cows. The effects of zone and breed on these traits are shown in table 4.  Heifers in the L zone had earlier AFC than those of zone M (28.9 vs. 32.5 months). Although interaction between zone and breed occurred, breed did not affect AFC of heifers in the L zone; but in the M zone its effect was 1.1 months (p<0.01). The AFC of the C heifers at the L and M zones was 28.8 and 33.56 months respectively, which the former was almost similar to that reported by Dong and Hieu (1995), but the latter was 4.96 months longer. The AFC of the Y heifers was 29 and 31.36 months respectively for the L and M zone, which were comparable with the findings of Duong et al (1995).    

AFC is favourably related to age at puberty (Galina and Arthur 1989). Previous reports indicated an average age at puberty of 19 months for the Y heifers, ranging from 16 to 24 months and an average of 21 months for C heifers, ranging from 19 to 29 months (Duong et al 1995). Delayed puberty in the C heifers was recognised as one important factor affecting lifetime reproductive performance of this breed. The Y heifers were younger at first calving than that of the C heifers, especially in the M zone because they were well adapted to the harsh environment in the central region of Vietnam.

The effect of zone on TPA was –0.49 month (p<0.001). Breed had no effects on TPA in the L zone. However, in the M zone the C cows were 1.64 months later in TPA than the Y cows (p<0.001).

CI is a combined trait reflecting reproductive performance of cows. The difference of CI mainly comes from the difference in TPA, because GL is rather stable. Zone affected CI (p<0.001), which CI of cows in the L and M zones, respectively, was 12.12 and 13.1 months. In the L zone breed had no effect on CI but it did in the M zone, 0.82 month (p<0.001). The average CI of the C cows in the L and M zones was 12.23 and 13.88 months respectively, which were 0.17 month shorter and 1.38 months longer than the findings of Dong and Hieu (1995). The average CI of the Y cows in the L and M zones was 11.9 and 12.18 months, which are in agreement with the finding of Thanh et al (1998), 12 months. Our finding is consistent with that of Bourdon and Brinks (1983), Duarte-Ortuno et al (1988) mentioned that the local cattle have shorter CI than those of exotic and crossbred breed.

GL was on average for species and breed, 282.33 days. The variation between zone and breed was small. However, the effect of zone on GL was significant, 0.61 day (p<0.001). Breed had no effect on GL (p>0.05).

Discussion 

Livestock in general and cattle in particular are an integral part of mixed farming system in Quang Ngai. Traditionally, farmers raise cattle for long-term savings, utilising agricultural by-products and natural grasses for draught power, manure and meat. Cattle are multi-purpose animals. Since the Opening Policy (Changing from central economy to market economy), the living standard of people was improved remarkably, which created demands for a higher amount and better quality of beef (Edson 1996). However the Y cattle are smaller at mature size and grow more slowly  (Duong et al 1995; Noi and Ly 1995; Thuong 1995). In that situation one of the common ways to improve beef production and create a genetic resource for milk production in the future is through the so-called cattle improvement program by importing Red Sindhi (Zebu), and other Zebu breeds, as well for crossbreeding with the native breeds. 

However, an important issue in crossbreeding, genotype x environment interaction is required for further research (Khan 1994). The level of G x E interaction depends on zone, production system + weather and climate (Holmes et al 1992; Vercoe and Frish 1992; Chaudhry et al 1994). G x E interaction is less clear, if the crossbreeding experiments are conducted at stations or at farms, where feeding practices and management are conditioned. These conditions seem to be far over the reach of most of Quang Ngai’s farmers. Therefore, the literature gave evidence for G x E interactions on productive and reproductive traits of the crossbred cattle.

C cattle had higher growth/month than the Y cattle in the L zone (2.34 vs. 2.16 cm CG/month), which is expected because the feeding practices and management in the L zone were good and met the demands for the growth of the C cattle. However, in the M zone the C cattle had lower growth/month than that of the Y cattle (2.15 vs. 2.20 cm CG/month). This indicates that the C cattle in the M zone were not fully meeting their demands for growth due to the limitations of feeding and management of the extensive production system. Huge differences in the CG growth of the C cattle at the two zones indicate the result of the GxE interaction on the C cattle.

GxE interaction also occurred in the reproductive traits, which can be seen in figure 1. It can be seen from the figure that in the L zone breed had no effects on the reproductive traits. However, in the M zone the Y cows had a better reproductive performance than the C cows.   

In general, the reproductive traits are lowly heritable. Thus, differences in the reproductive performance among herds are virtually all due to the environment and management. In the L zone, where feeding practices, and management are rather good / intensive, the C cows were able to meet demands for their growth and development, therefore their reproductive viability was comparable with the Y cows. However, in the M zone, where the cattle production system is extensive, our results support the hypothesis that the Y cows were reproductively adapted to this harsh environment through an earlier age at first calving of heifers, sooner time till pregnant again, and shorter calving interval of cows.

Y cattle have smaller maintenance requirements, which may signify an advantage in coping with adverse environmental conditions in the M zone (Maule 1973). In addition, because of the interaction between body size and forage plant ecology, small cattle may be more able to select feed for their productive and reproductive activities than the larger ones, especially in the dry season (Demment and Van Soest 1985) cited by (Carvalheira et al 1995). This advantage contributed to the better growth and reproductive viability of the Y cattle over the C cattle in the M zone.

Therefore, under the animal level judgement, the Y cattle should be preferred keeping in the extensive production systems such as in the M zone. The use of the C cattle should be carefully considered in combination with feeding practice and management. The C cattle should be kept in the production systems where the farmers are able to afford the extra expenses on concentrates and veterinary medicines, such as in the L zone.

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Received 14 December 2007; Accepted 7 November 2008; Published 1 February 2009

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