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* Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Private Bag 11-222, Palmerston North, New Zealand
Livestock Improvement Corporation, Private Bag 3016, Hamilton, New Zealand
Department of Animal Sciences, Colorado State University, Fort Collins 80523
1 Corresponding author: Jeremy.Bryant{at}agresearch.co.nz
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ABSTRACT |
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Key Words: genotype by environment interaction • multibreed • heterosis
The performance of dairy breeds in different environments has been evaluated in a number of recent studies (Dillon et al., 2003; Nielsen et al., 2003; Demeke et al., 2004). These studies have shown that not all breeds perform equally in each environment. Furthermore, crosses among breeds can result in significant improvements in production and survival traits over the average of the parental breeds (heterosis) incurring economic benefits (Swan and Kinghorn, 1992; López-Villalobos et al., 2000a; McAllister, 2002; VanRaden and Sanders, 2003). Environment has also been shown to influence the expression of heterosis, further complicating the estimation of crossbred performance (Barlow, 1981). Genetic evaluation of New Zealand dairy cattle is undertaken using a multibreed animal model, analyzing all breeds and breed crosses simultaneously. Breeding value estimates are on one scale allowing direct comparison of individual animals regardless of breed with heterogeneous variance accounted for in the applied statistical model (Harris et al., 1996, 2006). The objective of the current study was to quantify if environment within New Zealand influenced the expression of breed and heterosis effects.
A total of 184,288 first-lactation (2-yr-old) records of milk, fat, and protein yield from straight and mixed breed animals were used in this analysis (for full details see Bryant et al., 2007). The data represented 13 yr of progeny test records from 1989 to 2002, a total of 5,554 herd-year-seasons and daughters from 3,643 sires. Environmental data were matched to each record, and character state environments were then formed for herd-average total lactation yield of fat plus protein (MS), heat load index (HLI), herd size, and altitude. Character state averages were 227, 263, 305, and 376 kg per cow for herd-average MS yield; 61.4, 64.7, 67.2, and 69.6 for HLI; 154, 263, and 414 cows per herd for herd size; and 50, 178, and 367 m above sea level for altitude. The HLI of 61.4 and 69.6 are approximately equivalent to average summer maximum temperatures of 19 and 25°C at 80% humidity. A univariate multibreed sire model was applied within each environmental character state with the fixed effects of herd-year-season, second-order polynomial regressions on age at parturition (in months), linear regression on parturition date deviation from the mean herd-year-season parturition date, linear regressions on breed proportions [New Zealand Friesian (NZF), overseas Holstein-Friesian (OHF), New Zealand Jersey (NZJ), and other], heterosis, and recombination coefficients between the breeds. Confidence intervals at the 95% level (µ ± 1.96 standard error) were used to test if heterosis effects differed between character states and were significantly different from zero.
Overall, OHF cattle achieved the highest milk and protein yields in all environments, with NZJ cattle producing the lowest milk and protein yields. The highest fat yields of all breeds were in NZF cattle, with NZJ cattle producing the lowest yields of fat (Figure 1
). A scaling effect for milk, fat, and protein yield was observed in relation to MS yield (or nutritional environment) for the OHF and NZJ breeds. The differences for milk, fat, and protein yield between these breeds were 561, 1.3, and 9.3 kg, respectively, at 227 kg of MS/cow, much smaller than the differences of 1,151, 3.1, and 23.0 at 376 kg of MS/cow. Oldenbroek (1988) also observed that the difference in milk, fat, and protein yields and feed intake between Jersey and Friesian cattle was greater on a concentrate than on a roughage diet. Our results suggest that OHF, traditionally managed and selected in an intensive feeding system, are better suited to a high MS yield environment than NZJ, which were traditionally selected for performance on a pasture-based diet.
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). Heterosis levels for OHF x NZJ were greater in intermediate (263 and 305 kg of MS per cow) than in low (227 kg of MS per cow) and high (376 kg of MS per cow) MS yield environments; similar results were observed in intermediate HLI environments for protein yields. Heterosis levels for OHF x NZF were suppressed in very low MS yield environments and in many cases were not significantly different from zero. Heterosis was suppressed in crosses with OHF in the high HLI (69.6 HLI) environment. An HLI of 69.6 is approximately equivalent to average summer maximum temperatures of 25°C, humidity of 75%, wind speeds of 2 m/s, and a black globe temperature of 27.5°C or a temperature-humidity index of 74. Heterosis for fat yield for the crosses between OHF and NZF was not significantly different from zero in the high HLI and low MS yield environments, whereas in the other HLI and MS environments, the levels of heterosis expressed were significant and ranged from 2.0 to 3.2%. Limited heterosis for fat yield in crosses between OHF and NZF was observed at high altitudes. Estimates of recombination loss were mostly positive; however, few were significantly different from zero (results not shown).
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Barlow (1981), in a comprehensive review of different species, found that expression of heterosis is dependent on the environment in which breed crosses are managed (i.e., heterosis x environment interaction), and is generally greater in a stressful environment than in a supportive environment. However, as with this study, the natures of heterosis x environment interactions vary and definite conclusions on environment-dependent expression cannot be made. Heterosis for crosses with OHF cattle may have been suppressed in high HLI and low MS environments due to an elevated metabolic rate of the hybrid animals, thereby initiating the earlier onset of heat-stress effects on performance. Alternatively, nutrient supply in low MS yield herds may have been insufficient to allow expression of heterosis in the crossbred cows, which were genetically capable of high yields.
The expected performance in each environment of the major breeds and first breed crosses are presented in Figure 3. In most cases, 2-yr-old animals of OHF origin achieved the highest milk and protein yields compared with the other straight or crossbred animals. However, there were minimal differences between the milk and protein yield performance of OHF and OHF x NZF due to the expression of heterosis effects in the latter breed. In certain cases, the breed crosses of OHF x NZF and OHF x NZJ achieved greater protein yields than OHF due to the degree of heterosis expressed. Crossbred animals (OHF x NZJ, OHF x NZF, or NZF x NZJ) generally achieved higher fat yields compared with any of the straight breeds, which is consistent with the findings of López-Villalobos et al. (2000b). Using a system that penalized milk yield, rewarded fat and protein yield, and accounted for greater feed costs of larger animals (OHF and NZF) compared with smaller animals (NZJ), López-Villalobos et al. (2000b) estimated that the greatest profit would be achieved from straight crosses between Friesian (OHF and NZF) and NZJ. Based on the production estimates obtained in the present study, this is probably still the case. However, a mating scheme in which Friesian cattle are crossed with NZJ requires careful management to ensure heterosis effects are retained in subsequent generations. Heterosis retention may be achieved by mating crossbred sires with the first-cross animals, or by adopting a rotational crossbreeding strategy (López-Villalobos et al., 2000b).
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ACKNOWLEDGEMENTS |
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TOPABSTRACTACKNOWLEDGEMENTSREFERENCES |
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Received for publication June 21, 2006. Accepted for publication November 6, 2006.
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This article has been cited by other articles:
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  M. K. Sorensen, E. Norberg, J. Pedersen, and L. G. Christensen Invited Review: Crossbreeding in Dairy Cattle: A Danish Perspective J Dairy Sci, November 1, 2008; 91(11): 4116 - 4128. [Abstract] [Full Text] [PDF]
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B. J. Heins, L. B. Hansen, A. J. Seykora, D. G. Johnson, J. G. Linn, J. E. Romano, and A. R. Hazel Crossbreds of Jersey x Holstein Compared with Pure Holsteins for Production, Fertility, and Body and Udder Measurements During First Lactation J Dairy Sci, March 1, 2008; 91(3): 1270 - 1278. [Abstract] [Full Text] [PDF]
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), New Zealand Jersey (
), and other (
) for (a) milk yield, (b) fat yield, and (c) protein yield in relation to production level of fat plus protein (MS yield), heat load index (HLI), herd size, and altitude.
) for (a) milk yield, (b) fat yield, and (c) protein yield in relation to production level of fat plus protein (MS yield), heat load index (HLI), herd size, and altitude.
), New Zealand Jersey (NZJ; 
), OHF x NZF (+), OHF x NZJ (x), and NZF x NZJ (–) for (a) milk yield, (b) fat yield, and (c) protein yield in relation to production level of fat plus protein (MS yield), heat load index (HLI), herd size, and altitude.