|BROWN JR., A - University Of Arkansas|
|REITER, S - University Of Arkansas|
|JOHNSON, Z - University Of Arkansas|
|NABHAN, I - University Of Arkansas|
|LAMB, M - University Of Arkansas|
|STARNES, A - University Of Arkansas|
|ROSENKRANS JR, C - University Of Arkansas|
Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/29/2010
Publication Date: 8/11/2010
Citation: Brown Jr, A.H., Reiter, S.T., Brown, M.A., Johnson, Z.B., Nabhan, I.A., Lamb, M.A., Starnes, A.R., Rosenkrans Jr, C.F. 2010. Effects of heat shock protein-70 gene and forage system on milk yield and composition of beef cattle. Professional Animal Scientist. 26:398-403
Interpretive Summary: Heat shock proteins (HSPs) are a family of proteins from genes that activate in response to various stressors such as heat, cold, oxygen and food deprivations. Changes in heat shock protein gene might have an impact on milk yield and milk content. Milk yield is a trait controlled by many genes, each one of them with small effects. The mammary gland needs efficient physiological mechanisms involving multiple genes to synthesize milk during the course of lactation. Factors such as ambient temperature, toxins, or inflammation can adversely affect milk yield. Forage type such as a warm-season common bermudagrass (BG) or a cool-season endophyte-infected tall fescue (E+) tend to vary greatly in forage quality and quantity which influences metabolic status and performance of beef cattle. Cattle breed type also influences growth rate, reproductive efficiency, and maternal ability; therefore, selecting appropriate breeds that can adapt to stressful environments is an important decision for beef cattle producers. Effects estimated for genetic types in the bovine heat shock protein 70 gene and forage type on milk yield were sufficiently large in size for application in adaptation of cattle genotype to forage environment. Molecular diagnostics available to distinguish among these genetic types will allow the use of genotypic information for direct selection of adapted beef cattle at the population level. Genetic type x month effects were especially pronounced for somatic cell count and thereby strongly influenced the quality of milk. From the biological point of view, analyzing quantitative trait variation into variation caused by genes of known function will provide new insights into metabolic pathways and will help to further understanding of lactation physiology.
Technical Abstract: Genomic DNA from 117 Angus, Brahman, and reciprocal-cross cows was used to determine the influence of heat shock protein 70 haplotype and forage type [endophyte-infected tall fescue (Neotyphodium coenophialum; E+) or common bermudagrass (Cynododactylon; BG)] on milk yield and composition (protein, fat, and somatic cell count). Blood samples (n = 117) were collected, buffy coat separated, and genomic DNA extracted. A 523 bp fragment of HSP-70 gene was amplified by polymerase chain reaction purified, and sequenced to determine the single nucleotide polymorphisms (SNPs). Two of eight previously determined SNPs (at base 1926 as a C>G base substitution with a frequency of 3.8% and at base 2033 as a G>C base substitution with a frequency of 14%) were found to be functional and in the coding region. Cows were grouped based on pre-determined SNP profiles as haplotype 1 [24 Angus (AA), 23 Brahman (BB), and 45 crosses (AB or BA)], haplotype 2 [8 Angus (AA), 5 Brahman (BB) and 6 crosses (AB or BA)], or haplotype 3 [2 Angus (AA) and 4 crosses (AB or BA)]. Milk yield and composition were determined on 5 dates in each of 3 yr during the grazing period (May through September). Mean milk yield was greater (P < 0.01) for cows grazing BG (average 5.2 ± 0.06 kg/d) compared with cows grazing E+ (average 3.7 ± 0.23 kg/d). Similarly, milk fat content was greater (P < 0.01) for BG cows (average 3.93 ± 0.21%) than E+ cows (average 3.20 ± 0.26%). Our data indicated a haplotype x forage interaction for milk yield (P = 0.10), and a haplotype x month interaction for somatic cell count (P < 0.05).