The Productivity and Nutritional Management of Breeding Japanese Black Cows According to Stocking Rates on No-fertilized Zoysia-dominated Grassland

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  • 無施肥のシバ優占草地放牧の黒毛和種繁殖成雌牛における放牧密度別の生産性と栄養管理
  • ムセヒ ノ シバ ユウセンソウチ ホウボク ノ クロゲワシュ ハンショクセイメウシ ニ オケル ホウボク ミツド ベツ ノ セイサンセイ ト エイヨウ カンリ

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Abstract

In order to establish a nutritional management method of grazing Japanese Black cows on Zoysia-dominated grassland on the basis of low cost and labor-saving beef calf production in consideration of aging cow-calf farmers and to draw up guidelines for the cattle productivity of grassland, the nutritional intakes and grazing periods without supplements, the plant height of Zoysia under condition of grazing pressure according to stocking rates of 0.5 to 1.5cows/ha, the grazing capacity, and the optimum stocking rates under fixed continuous grazing were investigated. Animals grazed 4.4-ha of Zoysia-dominated grassland with no fertilization at low, middle, and high stocking rates of 0.5, 1.0, and 1.5cows/ha in each year between 2001 and 2003. When the body weights of cows were lower than that at the start of grazing, cows were fed concentrate supplement in compensation for the weight loss by using the 2000 ed. of the Japanese Feeding Standard for Beef Cattle and the concentrates were increased up to 3kg/day on an as-fed basis. The amounts of the nutritional excess and deficiency of a 500kg cow according to stocking rates, grazing seasons, and the cow's nutritional level were presented in tabulated forms, and nutrition shortage was greater in total digestible nutrients (TDN) and phosphorus (P) than in crude protein (CP) and calcium (Ca). From the fact that the energy (TDN) shortage was greater in late grazing periods, the grazing periods without supplements in the Chugoku and Shikoku districts were determined : cows in the nutrition stage of maintenance are able to graze from mid-April until November under 0.5 and 1.0cows/ha, and until September under 1.5cows/ha ; cows in the nutrition stage of pregnancy are able to graze from mid-April until November under 0.5cows/ha, until October under 1.0cows/ha, and until August under 1.5cows/ha ; cows in the nutrition stage of lactation are able to graze until October under 0.5cows/ha, until September under 1.0cows/ha, and until June under 1.5cows/ha. The plant height of Zoysia was effective as a generalpurpose indicator of the nutrition shortage in areas except the Chugoku and Shikoku districts : heights of 5cm serve as a guide for the end of grazing for cows in the lactation stage ; heights of 4cm as a guide for the end of grazing for cows in the pregnancy stage ; heights of 3cm as a guide for the end of grazing for cows in the maintenance stage. The optimum stocking rates under fixed continuous grazing of no-fertilized Zoysia-dominanted grassland ranged between 0.5 and 1.5cows/ha in terms of grassland maintenance and cattle productivity. The average TDN intake from 0.5 to 1.5cows/ha was the equivalent of the TDN requirement of late stage of pregnancy (4.9 kg/cow/day). On a nutrient basis, the grazing enabled cows in the maintenance stage a sufficient supply of P requirements, and cows of all nutrition stages a supply of CP and Ca requirements. On a stocking rate basis, the grazing enabled cows in the maintenance or pregnancy stage a supply of the necessary requirements between 1.0 and 1.5cow/ha, and cows of allnutrition stages a supply of the necessary requirements between 0.5 and 1.0cow/ha. In the case of feeding supplements to cows, feeds with high TDN and P contents were considered to be effective for compensating for low TDN and P intakes from the grassland. The grazing capacity of the Zoysia-dominated grassland was estimated to be 283CD/ha from mid-April to November, and 257CD/ha to September. The stocking rates under which total TDN intakes (kg/day/10a) reached the maximum ranged from 1.0-2.0cows/ha according to grazing seasons. Under fixed continuous grazing, the maximum intake from mid-April until November was 239kgDM/10a and 119kgTDN/10a at stocking rates of 1.5cows/ha. The Zoysia production during the same period was estimated to be 372kgDM/10a and 185kgTDN/10a, the maximum use rate of which was 64%. The practices of arresting the grazing before feeding supplements in the late grazing period and of grazing pregnant cows in no need of heat detection or artificial insemination together with their calves are suggested as low cost and labor-saving nutritional management techniques.

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