The Environmental Factors on the Lamb Growth, Analytically Studied with Extra-Seasonal-Lambs : III. The Effects of Seasons on the Growth and Development

第1報,第2報において短日処理法および短日処理・ホルモン処理併用法により,合計27頭の子羊を季節外に生産したことを報告した.これらのうち21頭を常法により1年間(雌),6カ月間(雄)飼育し,その発育・成長および皮膚面積の発育を測定した,この結果を試験期間中に行なった正常羊の試験結果と併せ検討することにより,極めて明瞭に子羊の発育および成長に及ぼす季節の影響を解析することができたので報告する.

1. 生後3月令までの早期発育においては,正常羊と季節外生産羊との間に発育パターンに差違はみられなかった。このことから子羊の早期発育においては,内因的要因,母乳(主として同品種・系統では個体的要因に属しまた在胎中の母羊の栄養と関係する)その他の要因が外部環境より強力に作用すること,そしてこの時期がBRODY(1945)のいわゆるaccelerating-phaseと関連することを暗示している.

2. 三村(1956)の提唱した発育における屈析転向点としての3月令の意義は,秋季生産羊では4月令に延長されていたが,3月令以後春季環境にあったためと理解された.

3. 増体重および体長その他の成長において,3乃至4月令以後はその季節環境によりそれぞれプラス,マイナスの影響をみることができた.特に春季はプラス,夏季次いで冬季はマイナスに作用していた.体高比成長により検討した結果は体型にも影響することが知られた.

4. 皮膚面積増大率は発育における傾向と似ているが,より拡大して示される.

5. 季節外生産羊を産業的に生産できるなら,秋季生産羊が本試験の結果からみて,最も有利な発育・成長をとげるであろうことは興味ある知見と思われる.

In order to determine how the environmental factors would affect the growth and development of lambs and to consider whether the growth pattern as described by MIMURA (1956) would be the same or different for lambs produced in normal season and one produced outside the normal season, twenty-one lambs were selected and reared among twenty-seven lambs which had been produced outside the normal season reported by MIMURA (1959, 1964) with eight lambs produced normally. They were reared during twelve months by female and during six months by male. The growth in live weight and the development in linear measurements investigated along with the growing of lambs, and the skin area on the part which was tattooed on the mid-side of lambs by the method reported by BURNS (1935) and MIMURA (1956) was also measured and the growth investigated. After this the lambs were classified into five groups; spring lambs, early summer lambs, summer lambs, autumn lambs and winter lambs according to their lambing seasons, and the data were compared each other.

The results are as follows.
1. Although there are remarkably growth- differences after the the third month, a straight line shows until the lambs grow up to the third month, not only spring lambs but in other season lambs with the exception of autumn lambs. Autumn lambs grow up straight forward until the forth month.
2. The growth and development of lambs after about the 3rd month shows a considerably higher rate under spring condition, and a lower rate under summer condition followed by early autumn and winter conditions.
3. The results, therefore, indicate that the general pattern of growth and development suggested by MIMURA (1956) and the present experiments coincide, but that seasonal effects considerably affect the growth and development of lambs after the early stage. The remarkable decrease of growth rate, for example, in early summer lambs and summer lambs from the 4th to the 9th months against the clear increases from the 9th to the 12th months are pointed out.

The seasons of summer and early autumn in the west districts of Japan are characterized as hot and dry. The growth and development of lambs are suppressed not only by climatic effects, but mainly by nutritional fall in feeding under these seasons. Lambs in Japan are also under-feeding in winter.
4. It is very interesting to observe that the general pattern of growth in early stages was not affected by lambing seasons, probably due to unknown endogenous factors, milk supply and others would overcome the environmental factors. Concerning the exception with autumn lambs from the 3rd month to the 4th month, it must be considered that when the lambs after the 3rd month are under spring condition the decrease of growth rate will be relieved. Then it will be correct to say that the growth will slow down to about the third month or the fourth month, if one want to discuss the point of inflection of growth on the lambs produced all over a year.
5. There was a significant correlation between the expansion ratio of skin area on the part tattooed and the growth in live weight, although the expansion ratio changed during the growing of lambs on a larger scale than that of the growth.
6. From the investigation of specific growth rate, under summer condition suppressing influences were shown in body length, rump length and rump width of winter lambs, but under spring condition advantageous influences were shown in those of autumn lambs as compared with that of lambs produced under normal season.
7. It is very interesting to observe that from the present results autumn lambs will be most advantageous commercially if the lambs could be produced under treatment.