Sheep productivity

Indices of ewe productivity
Flock productivity

Indices of ewe productivity

The characters of reproductive performance, lamb viability, lamb weaning weight and ewe weight were combined to build three productivity indices. Index 1, the total weight of weaned lamb per ewe per year, was computed for each ewe parturition as the product of total weight of weaned lamb × 365 ÷ interval to next lambing. Index 2, the total weight of weaned lamb per kg of ewe per year, was computed as index 1 ÷ ewe average weight. Index 3, the total weight of weaned lamb per kg of metabolic weight of ewe per year, was computed as Index 1 ÷ ewe average weight ^.73. Data on 397 ewe parturitions were available from 1977 to 1980.

The significance of environmental influences on the three productivity indices is indicated in Table 27.

Table 27. Analysis of variance of productivity indices

Source	d.f.	Mean squares
		Index 1	Index 2	Index 3
			×10- 2	×10- 2
Origin	1	676**	5049**	1270**
Year of lambing	3	1270**	18474**	3702**
Month of lambing	11	88	1356	267
Type of lambing	1	426**	4464*	991*
Number of lambing/foundation	1	140	3916*	669*
Number of lambing/born on centre	2	499**	7244**	1479**
Remainder	377	55	889	172

*=P< 0.05. ** =P< 0.01.

The estimated least squares means for productivity indices are laid out in Table 28.

Table 28. Estimated least squares means of productivity indices

Variable	Number	Index 1	Index 2	Index 3
Overall mean	397	11.49	465.84	1103
Origin
Foundation (1)	229	12.95	505.82	1211
Born on centre (2)	168	10.02	425.85	995
Year of lambing
1977	51	13.57	566.47	1332
1978	141	6.45	265.30	626
1979	107	10.78	452.19	1060
1980	98	15.15	579.38	1394
Month of lambing
January	18	11.46	470.43	1117
February	37	8.90	375.07	877
March	43	11.40	463.10	1096
April	25	13.67	555.59	1316
May	33	13.28	555.74	1304
June	31	10.07	533.10	1259
July	10	10.61	413.84	991
August	7	5.61	230.81	545
September	28	12.57	500.92	1192
October	46	11.39	470.20	1109
November	60	13.59	544.46	1292
December	59	12.28	476.76	1144
Type of lambing
Single	348	9.82	411.81	966
Twin	49	13.16	519.86	1240
Number of lambing/origin 1
1-4	112	13.94	558.17	1327
5+	117	11.96	453.48	1095
Number of lambing/origin 2
1	66	7.25	324.09	745
2	48	9.46	397.14	931
3+	54	13.38	556.33	1310

The mean productivity indices were:

Index 1.	11.5 kg of weaned lamb per ewe per year
Index 2.	466 gm of weaned lamb per kg of ewe per year
Index 3.	1103 gm of weaned lamb per kg .73 of ewe per year.

Year of lambing had very significant effects on productivity. This would be expected, following the major year effects previously found on the different performance traits making up the productivity indices.

Type of lambing had an effect on productivity, ewes producing twins being 34%, 26% and 28% superior to those producing singles, for indices 1, 2 and 3 respectively. This was in spite of the lower individual weaning weights and higher mortality in twin lambs compared with singles.

The effect of parturition number of ewes born on the centre was highly significant, ewes with 3 or more parturitions being 84%, and ewes with 2 parturitions being 30% superior to first parturition females for index 1. Corresponding figures for index 2 were 71% and 22%, and for index 3, 75% and 24%.

Flock productivity

Adjustment of the three ewe productivity indices to account for actual twinning rates found (12%) and actual ewe viability rates (85.2%) give the most accurate estimates of overall flock productivity. These are:

Index 1:	8.7 kg of weaned lamb per ewe per year
Index 2:	362 gm of weaned lamb per kg of ewe per year
Index 3:	850 gm of weaned lamb per kg .73 of ewe per year.