7. Breed and environmental effects on productivity levels

7.1 Summary of the production potential of the five sites
7.2 Productivity of different breeds and crosses
7.3 Rainfall effects
7.4 Seasonal variation
7.5 Year effects
7.6 Parturition effects

7.1 Summary of the production potential of the five sites

In the broadest sense, the five sites covered in this study can be considered as five different production environments, including factors of climate, soil fertility, management, nutritional supplementation and intensity and type of output demanded. These production factors have been described in the chapters on the individual sites. Using all objective measures available, plus the subjective knowledge contributed by the owners and managers of these ranches, the current production potential of each site has been evaluated under the specific management regimen currently in practice.

Over a period of time, all five ranches have introduced Sahiwal cattle, and various combinations of the Sahiwal breed with exotic Bos taurus and local Bos indicus breeds have been examined. In some cases the productivity of pure Bos taurus cattle has also been compared. It can be argued that each ranch has moved towards the broad genetic types most suited to its particular environmental situation and production system, and the best estimate of the current production potentials of the sites would appear to be the productivity index of the breeding groups most suited to each. The calculation of these indices has already been described: the characters of reproductive performance, cow and calf viability, milk production, growth and cow body weight are combined to provide the total weight of 1-year-old calf plus the liveweight equivalent of milk produced, both per cow per year and per 100 kg of cow maintained per year.

Table 18 indicates the present production potential of each of the five sites, ranging from 64% to 145% of the overall average. These production potentials provide a broad ranking of the situations within which the influence of troth genetic and environmental factors can be examined.

Table 18. Summary site descriptions

	Ilkerin	El Karama	Cedarvale	Deloraine	Kilifi
Annual rainfall (mm)	610	691	682	1007	1043
Elevation (m)	2200	1800	2000	2100	10
Annual potential evaporation (mm) (Woodhead, 1968)	1700	1900	1700	1900	2300
Pastures	natural	natural	seeded/natural	seeded/natural	natural
Estimated stocking rates	medium	medium	high	medium	high
Major products	milk/meat	meat	milk/meat	milk/meat	milk
Supplementation	low	nil	low	medium	high
Breed type with greatest output at present	Sahiwal	Sahiwal	Sahiwal/Ayrshire combinations	Sahiwal/Ayrshire combinations	Sahiwal/Ayrshire combinations
Productivity index/cow for most productive breed type	160	190	278	267	364
Productivity index relative to average for 5 sites (%)	64	75	110	106	144

7.2 Productivity of different breeds and crosses

Ilkerin has the lowest rainfall and a low and highly variable nutritive status. The data show that the Sahiwal breed is adapted to these conditions and is markedly superior to the Small East African Zebu in both milk production and growth rate. The 38-day shorter calving interval demonstrates the fitness of the Sahiwal breed in this environment.

El Karama has relatively low rainfall and desiccating winds which reduce the moisture available for plant growth. The area is also subject to droughts, a major reason for the emphasis on beef production. The results from this situation provide excellent comparative data on the Sahiwal and Boran breeds as straight-breds in a beef production environment.

The Sahiwal breed at El Karama proved superior to the Boran in maternal ability, whereas the Boran was probably superior in genetic merit for growth. Boran heifers were 10% heavier than Sahiwal heifers at 21 months but cows of the two breeds did not differ in mature weight. When account was taken of the milk that was extracted from the Sahiwal cows, they proved to be 9% superior to the Boran in terms of a productivity index per cow per year. The Boran breed has long been used as a standard of comparison in beef production programmes in eastern African locations with environmental conditions similar to El Karama: these results demonstrate that the Sahiwal is also well adapted to a beef production environment.

The three higher-potential sites, Cedarvale, Deloraine and Kilifi, all maintained pure Ayrshires, an exotic Bos taurus breed, at some stage, but only Deloraine Estates still maintains purebred Ayrshires today. Even though this site has a climatic environment to which pure exotic breeds of Bos taurus cattle are considered adapted, lying in the temperate highlands with 1000 mm mean annual rainfall, the nutritional levels available favour crosses of Ayrshire with Sahiwal. The Ayrshire-Sahiwal cross cows exceeded the pure Ayrshire cows by 4% in productivity index per cow per year in spite of the fact that the Ayrshires received preferential feeding. The milked-out lactation yield was 185 kg greater for the straightbred Ayrshire cows than for the Ayrshire-Sahiwal crosses: it was the higher calving percentage and greater calf survival rate of the Ayrshire-Sahiwal cross cows that accounted for their higher productivity index.

Cedarvale has relatively low rainfall, but some improved pastures have been provided and management factors are manipulated substantially in response to environmental conditions. On the basis of cow productivity indices, the three crosses of Ayrshire and Sahiwal showed an average superiority of approximately 50% over pure Sahiwals. The optimum contribution by the Sahiwal breed to a population also based on the Ayrshire breed is between one-fourth and one-half in this type of environment. The indications are that milk production will be reduced when the contribution by the Sahiwal breed exceeds one-half.

At Kilifi, ²/₃ Ayrshire - ¹/₃ Sahiwal cows outyielded ¹/₃ Ayrshire ²/₃ Sahiwal cows by 7% for full lactation and 4% on an annual yield basis. In terms of the productivity index, their advantage was 3%. The level of nutrition provided at this site was the best of the five situations studied and most probably approached the level necessary for maximum expression of genetic differences between breeding groups. However, the climate, with high temperatures and high relative humidity, was the harshest of the five sites. In conclusion, the optimum contribution by the Sahiwal breed for milk and beef production under relatively humid conditions without nutritive stress is probably somewhere between one-fourth and one-half, with the remainder contributed by Bos taurus breeds that possess relatively high milk production and growth capability.

7.3 Rainfall effects

It appears that the major effects of rainfall on herbage growth can best be ascribed to the total rainfall measured over the relevant period, commencing 1 month before the herbage quality affects the animals' performance. Table 19 illustrates the relationship between lactation yield and rainfall from 1 month before parturition until 1 month before the completion of lactation.

Table 19. Relationship between 'lactation yield and rainfall from 1 month before parturition until 1 month before the end of lactation

Sitea	Milk		Rainfall		Correlation ® and regression (b) of lactation yield (kg)/rain-fall (mm)
	(kg)	CV (%)	(mm)	CV (%)	r	b
Ilkerin Project	315	38	303	26	0.81	1.2
Cedarvale Farms	1666	16	412	28	0.63	1.4
Deloraine Estates	1057	8	753	11	0.47	0.5
Kilifi Plantations	2753	3	892	10	0.15	0.2
Overall					0.54	0.91

^a Excluding El Karama Ranch, where no milk is produced.

There was an overall correlation of 0.54 between lactation yield and rainfall during the relevant period, with the correlation tending to be higher in the areas of lower rainfall. Overall, 0.91 kg of additional milk was produced per 1. 0 mm of additional rainfall, ranging at the different sites from a high of 1.4 kg to a low of 0.2 kg per 1.0 mm.

Table 20 illustrates the relationship between weaning weight and rainfall during the period from birth to weaning. All three situations were similar, with an overall correlation of 0.92 between weaning weight and rainfall during the relevant period. The corresponding regression was 0.15 kg additional weight at weaning per 1 mm of additional rainfall.

Table 20. Relationship between weaning weight and rainfall from birth to weaning

	Weaning weight		Rainfall		Correlation ® and regression (b) of weaning weight (kg)/rainfall (mm)
Sitea	(kg)	CV (%)	(mm)	CV (%)	r	b
El Karama Ranch	170.4	5	464	13	0.92	0.12
Cedarvale Farms	163.3	9	509	16	0.83	0.14
Deloraine Estates	170.8	9	753	11	0.86	0.15
Overall					0.92	0.15

^a Excluding Kilifi Plantations, where calves were raised artificially and early weaned, and Ilkerin Project which did not have sufficient month-of-birth data.

Table 21. Relationship between calving interval and rainfall from 3 months before previous calving date to 1 month before conception

	Calving Interval		Rainfall		Correlation ® and regression (b) of calving interval (days)/rainfall (mm)
Sitea	(days)	CV (%)	(mm)	CV (%)
					r	b
El Karama Ranch	402	2	346	17	- 0.49	- 0. 08
Cedarvale Farms	424	1	370	29	0. 04	- 0. 01
Deloraine Estates	419	3	537	34	- 0.15	- 0.01
Kilifi Plantations	394	2	522	42	- 0. 24	- 0. 01
Overall					- 0.16	- 0.01

^a Excluding Ilkerin Project which did not have sufficient month-of-parturition data.

Table 21 illustrates the relationship between calving interval and rainfall from 3 months prior to the previous calving to 1 month before conception. The overall correlation of -0.16 between calving interval and rainfall during the relevant period was not significant; the corresponding regression was -0. 01.

Table 22 illustrates the relationship between calf survival to weaning and rainfall over the period from birth to weaning. The overall correlation of 0.08 between calf survival to weaning and rainfall during the relevant period was not significant.

Table 22. Relationship between calf survival to weaning and rainfall from birth to weaning

	Viability		Rainfall		Correlation ® and regression (b) of calf survival (%)/rainfall (mm)
Sitea	(days)	CV (%0	(mm)	CV (%)
					r	b
El Karama Ranch	95.1	2	464	13	- 0.03	- 0.001
Cedarvale Farms	79.4	7	509	16	0.13	0.003
Deloraine Estates	89.5	5	753	11	0.07	0.009
Overall					0.08	0.005

^a Excluding Kilifi Plantations where calves were early weaned and raised artificially, and Ilkerin Project which did not have sufficient month-of-birth data.

Thus, rainfall over the relevant period at the five locations had a positive effect on lactation yield and weaning weight, but no significant effect on calving interval or calf survival. Differences between the sites were only significant in the case of lactation yield: for this character, the effects of rainfall were most important in the drier locations.

7.4 Seasonal variation

Seasonal variation throughout the year, as represented by the range of values for six 2-month calving periods, was reflected in many situations in all important characters. Table 23 indicates that seasonal variation was greatest in milk production, growth, viability and reproduction in that order: for all the sites combined, the differences between best and poorest 2-month calving periods were 35% for milk production, 18% for growth characters, 15% for viability and 10% for reproduction. Overall, productivity showed a difference of 16% between the best and poorest 2-month periods. Seasonal variation was greatest at Cedarvale, Ilkerin, Deloraine, Kilifi and El Karama in that order: the differences between the best and poorest seasons in terms of overall productivity were 34% at Cedarvale, 20% at Ilkerin, 11% at Deloraine, 7% at Kilifi and 5% at El Karama.

In terms specifically of milk production, seasonal variation was 59% at Ilkerin, 45% at Cedarvale, 24% at Deloraine and 11% at Kilifi. Seasonal differences in growth as reflected by weaning weight were less marked, ranging from 24% at Deloraine to 19% at Cedarvale and 11% at Ilkerin. Viability as reflected by calf survival to weaning varied according to 2- month periods by 22% at Cedarvale, 14% at Deloraine and 4% at El Karama, while reproductive performance, as reflected by calving interval, varied according to seasonal factors by 18% at El Karama, 12% at Cedarvale, 9% at Deloraine, 6% at Ilkerin and 5% at Kilifi.

The information summarized in Table 23 indicates major seasonal variations in performance, both in terms of overall productivity and the individual components of the productivity index, at Cedarvale and Ilkerin. This variation is likely due to dependence on natural grazing in areas of relatively low rainfall and variable distribution over the year. Production at Cedarvale is affected more strongly by seasonal rainfall variability than at Ilkerin, due to the much higher level of offtake at the first site and the relatively high stocking rates. Production at Deloraine is less affected by seasonal variability than at Cedarvale and Ilkerin because stocking rates are lower and rainfall is much higher and less variable.

Table 23. Difference in performance characters between best and poorest seasons

		Ilkerin	El Karama	Cedarvale	Deloraine	Kilifi	Mean
Productivity index
	difference between best and poorest (%)	20	5	34	11	7	16
	CV (%)	6.9	1.7	10.7	4.4	2.4	5.2
Growth - weaning weight
	difference between best and poorest (%)	NA	11	19	24	NA	18
	CV (%)	NA	4.7	8.5	9.1	NA	7.4
Milk - lactation yield
	difference between best and poorest (%)	59	-	45	24	11	35
	CV (%)	38	-	15.6	7.6	3.4	16.2
Viability - calf survival
	difference between best and poorest (%)	NA	4	22	14	NA	15
	CV (%)	NA	1.5	7.3	5.0	NA	4.6
Reproductive performance calving interval
	difference between best and poorest (%)	18	6	12	9	5	10
	CV (%)	7.5	2.2	4.0	3.3	2.1	3.8

Kilifi Plantations is even less affected by seasonal rainfall variability: the high offtake rate at this site is more than compensated for by the high rainfall, improved pastures and relatively high levels of supplementary feeding. El Karama is least affected by seasonal rainfall distribution: though annual rainfall is not particularly high, offtake is low and rainfall distribution throughout the year is less variable than at any other site.

7.5 Year effects

Table 24 illustrates the variation between the best and poorest years for overall productivity and for the four main components of the productivity index. For the five sites, records were available over an average of 4.4 years. Overall, the index of cow productivity varied by 35% from the best to the poorest year. This effect was greatest for the lower-potential sites. Differences in productivity in different years were greatest in terms of lactation yield, followed by weaning weight, calving interval and then calf survival.

Table 24. Differences in performance between best and poorest years

		Ilkerin	El Karama	Cedarvale	Deloraine	Kilifi	Mean
Productivity index
	number of years	3	6	3	4	6	4.4
	difference between best and poorest(%)	60	48	26	24	18	35
	CV (%)	24	15.6	11.5	8.9	7.3	13.5
Growth - weaning weight
	number of years	3	6	3	4	NA	4.0
	difference between best and poorest (%)	23	27	9	26	NA	24
	CV (%)	12.0	9 0	4.2	14.3	NA	9.9
Milk - lactation yield
	number of years	3	NA	3	4	6	4.0
	difference between best and poorest (%)	28	NA	43	85	24	45
	CV (%)	12.7	NA	17.8	24.9	8.8	16.1
Viability - calf survival
	number of years	NA	6	3	4	6	4.8
	difference between best and poorest (%)	NA	9	5	11	9	9
	CV (%)	NA	3.5	2.3	4.8	2.9	3.4
Reproductive performance - calving interval
	number of years	3	6	7	4	6	5.2
	difference between best and poorest (%)	69	16	11	13	3	22
	CV (%)	26.2	9.1	7.2	5.9	1.1	9.9

7.6 Parturition effects

Table 25 illustrates the difference between first and best parturition for overall productivity and the four main components of the productivity index. Overall for the four sites included in this analysis, peak productivity was reached after the fourth parturition, averaging 28% more than productivity after the first parturition. This increase was similar at all four sites, irrespective of production potential. The major effects of parturition number were on milk yield, with weaning weight, calving interval and calf survival much less affected.

Table 25. Differences in performance between first and best parturition

		El Karama	Cedarvale	Deloraine	Kilifi	Mean
Productivity index
	difference between first and best parturition (%)	29	34	28	22	28
	best parturition number	6	4-5	3	5	4-5
Growth - weaning weight
	difference between first and best parturition (%)	4	11	4	NA	6
	best parturition number	3	6+	4	NA	4
Milk - lactation yield
	difference between first and best parturition (%)	NA	51	28	22	34
	best parturition number	NA	4-5	3	4	4
Viability - calf survival
	difference between first and best parturition (%)	8	15	7	NA	10
	best parturition number	6	6+	2	NA	5
Reproductive performance - calving interval
	difference between first and best parturition (%)	17	5	11	7	10
	best parturition number	6	4-5	3	9	5-6