Analysis of the effect of environmental factors on milk yield and composition, and reduction of environmental effects on the basis of lactation curves

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  • 乳量および乳成分率への環境の影響と泌乳曲線による環境要因の補正
  • ニュウリョウ オヨビ ニュウセイブンリツ エ ノ カンキョウ ノ エイキョウ ト ヒニュウキョクセン ニ ヨル カンキョウ ヨウイン ノ ホセイ

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Abstract

Milk production traits are affected by environmental factors, e.g., heat stress, region, calving month, and lactation number. The purpose of this study was to investigate the effects of these environmental factors on milk yield, fat percent, protein percent, and fat-to-protein rate (FPR), and to reduce these environmental effects on the basis of lactation curves. The data recorded comprised 13,364,965 test-day records from 889,035 Holstein cows in 11,257 herds from 2008 to 2010. The yields were divided according to 4 regions (1 : Hokkaido ; 2 : Tohoku ; 3 : Kanto, Hokuriku, Chubu, and Chugoku ; and 4 : Kinki, Shikoku, and Kyushu), 12 calendar months, and 4 parity groups (1 : first parity, 2 : second parity, 3 : third and fourth parities, and 4 : fifth and sixth parities). Day 120 after calving of second-parity cows at 36-37 months of age in Hokkaido in May was considered the standard condition. The equation of the standard lactation curve was a fifth-order Legendre polynomial with the Wilmink function. Test-day records of milk yield, fat percent, protein percent, and FPR were converted to standardized milk yield, standardized fat percent, standardized protein percent, and standardized FPR, respectively, by using the corresponding standard lactation curve. Region, calving month, and lactation number affected the shapes of the standard lactation curves of milk yield, fat percent, protein percent, and FPR. The seasonal changes of the shapes of standard lactation curves were cyclic. These standard lactation curves in each calving month differed by region and lactation number. In addition, in each lactation, all the standard lactation curves─except those for milk yield─differed by region. The standardized milk yields during September to December in 2010 were lower than those in the corresponding months in 2008 and 2009. These results suggested that the recovery of the cows from the influence of summer heat stress in 2010 was slower than that in 2008 and 2009. The standardized FPR at September in 2010 was lower than that in 2008 and 2009, because the increment in the standardized fat percent was smaller than the increment in standardized protein percent. This indicated that the recovery of normal roughage intake was delayed compared to the recovery of normal total intake after summer heat stress in 2010. The standardized fat percent, standardized protein percent, and standardized FPR reflect the total intake, roughage intake, and energy balance. Therefore, such standardized records might provide useful information for herd management to dairy farmers.

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