Oct. 



Fertility in Shropshire Sheep 



233 



lambing season. To test this point Table III was made, showing the 

 month of birth and the percentages of singles, twins, and triplets. It is 

 readily seen that a larger percentage of twins is bom early in the season 

 than is bom later. Of the 3,790 lambs bom in January, February, and 

 March 42.3 per cent are twins, while of the 4,617 born in April, May, 

 and June only 36.1 per cent are twins. If the triplets are added in with 

 the twins the percentages are 43.1 in multiple births for January, 

 February, and March, and 36.7 for April, May, and June. As Heape (5) 

 points out, this may be due to the ewes with the most vigorous and active 

 generative systems coming into heat earlier in the season. This may 

 be also affected by the fact that early in the breeding season more 

 green feed is available, a factor influencing the number of twins pro- 

 duced. 



Table; lll.—Months of birth {Shropshires) 



Month. 



January. .. 

 February. . 



March 



April 



May 



June 



August. .. . 

 September 

 December, 



Total 

 number. 



33 



471 



3,286 



3.615 

 966 



36 



Percentage 

 of singles. 



75-8 

 56.7 

 56.7 

 62.4 

 66.3 



75-0 

 100. o 

 100. o 



Percentage 

 of twins. 



24.2 



43-1 

 42.4 



37-0 

 32.9 

 25.0 



Percentage 

 of triplets. 



In the hope that additional information might be obtained, a study 

 was made of the Dorset breed (j), which produces a large number of 

 young in the fall. Table IV gives the month of lambing and the percent- 

 ages of singles, twins, triplets, quadruplets, and of all multiple births. 



Table lY.— Months of birth (Dorsets) 



Month of birth. 



January. . 

 February . 



March 



April 



May 



June 



July 



August. . . . 

 September 

 October. . . 

 November , 

 December . 



Total num- 

 ber. 



Percentage 

 of singles. 



1,818 

 2,386 



3.919 

 2,366 



857 



296 



90 



102 



925 

 1.546 

 1,088 

 1,418 



16,634 



61.5 

 54-3 

 52.7 

 51-7 

 ';4.8 



59-8 

 65.6 

 68.6 



73-7 

 66.2 

 67.7 

 61.0 



57-8 



Percentage 

 of twins. 



37-1 

 41.9 



43-9 



45-4 

 43-1 

 38.5 

 27.8 



30-4 

 25-3 

 32.9 

 30-5 

 36.8 



39-7 



Percentage 

 of triplets. 



1-3 

 3-8 

 3-2 

 2.6 

 2.1 



1-7 

 6.6 

 i.o 

 •9 

 •9 

 1.8 

 2.2 



2.4 



Percentage 

 of quad- 

 ruplets. 



Percentage 



in multiple 



births. 



38.S 

 45-7 

 47-3 

 48.3 

 45-2 

 40.2 



34-4 

 31-4 

 26.3 

 33-8 

 32.3 

 39-0 



42.2 



