5. Weight and growth

Introduction
Birth weight
Weights from birth to weaning
Breeding cow weights

Introduction

A high growth rate is of economic importance for both beef and dairy enterprises. In the case of beef, animals that grow faster reach slaughter weight earlier and therefore overhead costs are lower. In the case of dairy animals, culling can be more rigorous and stock can be replaced earlier if growth rates are higher, as heifers can calve at a younger age and hence increase their lifetime productivity in terms of calves and milk.

At Um Banein, more emphasis has been placed in the past on milk production than on growth, except when particular station directors or researchers have had a special interest in aspects of growth and weight. While a complete series of birth weights is available, data on other weights tend to have been unevenly recorded over the life of the station. This chapter analyses the available data in order to provide results for comparison with future data, which should be more rigorously collected.

Birth weight

Birth weights of 3466 calves were recorded in the period 1957-84. The unadjusted mean and standard error were 23.2 ± 0.05 kg (range 8.0-43.0 kg) with a coefficient of variation of 13.4%. The frequency distribution of these weights is shown in Figure 14.

The management system at Um Banein has not allowed the use of an analytical model in which dams could be analyzed within sire groups. Separate mixed models were therefore used to analyze the influences of individual dams and sires on birth weight. The mean squares from the analysis of variance for the dam effects are shown in Table 8 and the least-squares means in Table 9. The mean squares from the sire analysis are shown in Table 10 and the least-squares means in Table 11.

In both series of analyses it was shown that month of birth did not have a significant influence on birth weight, while year-group, sex of young and age of the dam had significant effects. There were no significant effects of the dam on birth weight but there were highly significant differences due to the sire.

Male calves were significantly heavier than females at birth. Calves born during the period 1968-75 were generally heavier than calves born during other periods, but in the dam analysis calves born in the period 1981-84 were heavier than calves born in any period except 1968-71. In the sire analysis, calf birth weights declined from a peak in 1968-1971. In the dam analysis; calf birth weights declined from dams more than 10 years old, while in the sire analysis weights increased throughout the life of the dam.

Figure 14. Frequency distribution of birth weights of Kenana calves born at Um Banein.

Table 8. Mean squares from the analysis of variance for birth weight (dam model).

Source of variation	d.f.	MS
Dam	744	13.2***
Month	11	10.8
Year group	5	167.4***
Sex	1	1201.9***
Damage	9	26.5***
Error	1638	7.3

*** P<0.001.

Table 9. Least-squares means for birth weight of Kenana calves (dam model).

	Variable	n	(Kg)
Overall L.S. mean		2409	22.7
Month:	January	222	22.6
	February	206	22.7
	March	210	22.9
	April	210	22.3
	May	215	22.4
	June	180	22.7
	July	194	22.7
	August	153	22.8
	September	198	23.4
	October	195	22.6
	November	189	22.8
	December	237	22.3
Average S.E.			0.26
Year group:	1961-1963	55	20.8a
	1964-1967	308	21.3a
	1968-1971	548	23.8b
	1972-1975	680	22.9c
	1976-1980	545	22.6ac
	1981-1984	273	24.6b
Average S.E.			0.42
Sex:	female	1207	21.8a
	male	1202	23.5b
Average S.E.			0.14
Dam age (years):	<4	165	23.2a
	4 - 5	345	23.4a
	5 - 6	425	23.2a
	6 - 7	345	23.4a
	7 - 8	300	23.1a
	8 - 9	222	22.9a
	9 - 10	177	22.8ab
	10 - 11	140	22.1bc
	11 - 12	103	21.6cd
	>12	187	21.1d
Average S.E.			0.29

Within variables means without a common superscript differ significantly (P<0.05).

Table 10. Mean squares from the analysis of variance for birth weight (sire model).

Source of variation	d.f.	MS
Sire	90	19.1***
Month	11	11.6
Year group	5	108.2***
Sex	1	1635.4***
Dam age	9	42.9***
Error	2292	8.8

*** P<0.001.

Table 11. Least-squares means for birth weight of Kenana calves (sire model).

Variable		n	(Kg)
Overall L.S. mean		2409	23.2
Month:	January	222	23.1
	February	206	23.2
	March	210	23.5
	April	210	23.2
	May	215	22.9
	June	180	23.2
	July	194	22.8
	August	153	23.3
	September	198	23.7
	October	195	23.4
	November	189	23.2
	December	237	23.0
Average S.E.			0.29
Year group:	1961-1963	55	23.9ab
	1964-1967	308	23.8a
	1968-1971	548	24.7b
	1972-1975	680	23.4a
	1976-1980	545	22.2c
	1981-1984	273	21.1d
Average S.E.			0.38
Sex:	female	1207	22.3a
	male	1202	24.1b
Average S.E.			0.21
Dam age (years):	4	165	22.1a
	4 - 5	345	22.5ab
	5 - 6	425	22.9bc
	6 - 7	345	23.6cd
	7 - 8	300	23.5cd
	8 - 9	222	23.5cd
	9 - 10	177	23.5cd
	10 - 11	140	23.3bcd
	11 - 12	103	23.2bcd
	>12	187	23.9d
Average S.E.			0.29

Within variables means without a common superscript differ significantly (P<0.05).

Repeatability of birth weight (as a trait of the dam) was found to be 0.200 ± 0.022. Heritability (estimated as a trait of the sire) was 0.190 ± 0.048.

The mean birth weight found in this study is less than that reported by Khalifa and Khalafalla (1979) but slightly heavier than that reported by Hattersley (1951) for Kenana cattle. Male calves in the current study were 1.7 kg heavier than female calves, compared with an earlier difference of 1.3 kg (Khalifa and Khalafalla, 1979). The decline in birth weight from 1968 to 1971 can be attributed to shortage of feed due to the high stocking rates during those years (c.f. Figure 6). The effect of dam age on birth weight in the sire analysis in this study is in agreement with that found by Khalifa and Khalafalla (1979), who reported that birth weight tended to increase with age of dam, reaching a maximum in cows more than 7.5 years old.

The heritability and repeatability of birth weight in this study estimated at 0.190 ± 0.048 and 0.200 ± 0.022 respectively were lower than those reported by Khalifa and Khalafalla (1979). This could be due to the deterioration of management and fluctuation of environmental conditions in the period 1972-84.

Weights from birth to weaning

Calf weaning weights
Calf body weights from birth to 180 days
Calf growth rate from birth to 180 days
Phenotypic correlations at different ages for body weight and growth rate

Weight measurements after birth were made on calves born in 1958 and 1959, in 1978 and then from 1980 onwards. The earlier measurements were made on calves born of foundation dams and the later ones on calves of station-bred dams. The later weights were taken following a long period of overstocking and during a prolonged drought. It should therefore be recognized that the observed weights are probably lower than long-term weights would be and that growth rates would also be lower.

Calf weaning weights

The unadjusted mean and standard error of weaning weight at 120 days for calves born in 1980 to 1984 were 52.4 ± 0.57 kg with a coefficient of variation of 22.3%.

Table 12 presents the mean squares from the analysis of variance for weaning weight. Only the sex of the calf and year of birth had significant effects on this trait. Season of birth and dam age showed no significant effect on weaning weight.

Least-squares means of weaning weight are shown in Table 13. Calves weaned in 1983 and 1984 were significantly heavier than those weaned in other years. Males were significantly heavier than females. There was a slight but non-significant increase in weaning weight as dam age increased.

Table 12. Mean squares from the analysis of variance for 120-day weaning weight.

Source of variations	d.f.	MS
Season of birth	2	43 402
Year of birth	4	45 517*
Sex	1	192 126**
Dam age	9	19 231
Error	323	21 085

<0.05; *+ P<0.01.

Table 13. Least-squares means of 120-day weaning weight of Kenana calves.

Variable		n	(Kg)
Overall L.S. mean		340	51.2
Season:	winter	155	51.0
	hot summer	65	51.9
	wet summer	120	50.6
Average S.E.			2.39
Year:	1980	55	50.3a
	1981	73	49.0a
	1982	69	48.0a
	1983	77	52.4b
	1984	66	56.1b
Average S.E.			1.60
Sex:	female	182	49.5a
	male	158	52.8b
Average S.E.			1.07
Dam age (years):	<4	4	41.5
	4 - 5	14	47.3
	5 - 6	48	50.8
	6 - 7	36	52.9
	7 - 8	33	53.2
	8 - 9	29	51.1
	9 - 10	39	51.8
	10 - 11	36	52.9
	11 - 12	33	56.2
	>12	68	53.8
Average S.E.			2.40

Within variables, means without a common superscript differ significantly (P<0.05).

In a trial carried out on the station, weight gains and growth rates of calves weaned at 60 days of age were compared with those of calves weaned at 120 days. Table 14 shows the least-squares analysis of variance of this comparison while least-squares means of body weight and daily gains are shown in Table 15 for the two different groups. It is clear from these two tables that early weaning did not affect subsequent growth up to the age of 120 days.

There are, apparently, no earlier comparative data available on the weaning weights of Kenana calves.

The high weaning weights in 1983 and 1984 are due to these calves being fed green legumes and concentrate ad lib from the age of 1 week onwards. Male calves outweighed female calves by 2.8 kg and this could be due to the fact that the calves that were heaviest at birth were heaviest at weaning (Mukhtar, 1961; Osman and Rizgalla, 1968). The absence of significant effects of season and dam age on this trait is as expected, since calves were artificially reared.

Early weaning (60 days) did not affect subsequent growth of calves at least until the age of 120 days. In this case, liquid milk could be saved for human consumption and farmers would be able to sell the surplus to maximize profit. A 60 day-old calf weighing 35.5 kg consumes 2.2 kg of milk per day (Table 2). If this amount were saved and sold, it would provide an income of LSud 3.74 per cow per day if sold at the Khartoum market price of LSud 1.70 per litter (LSud 3.00 = US$ 1.00).

Calf body weights from birth to 180 days

Data for growth rate from birth to 180 days of age were available for 156 calves (97 males and 59 females) born from 1980 to 1984.

Mean squares from the analysis of variance for body weights from birth to 180 days of age are shown in Table 16. Season of calving had a significant effect on birth weight only and did not affect weights at older ages. Year of calving affected birth, 30-day, 60-day and 90-day weights significantly. Sex had a significant effect on both birth weight and 30-day weight. Dam age had a significant effect only on birth weight.

Least-squares means of body weights from birth to 180 days of age are given in Table 17. Calves born in winter had significantly higher birth weights than those born in the hot and wet summers. Season had no significant influence on body weights from 30 days up to 180 days. Year of calving affected body weights from birth to 180 days in an increasing pattern, being low in 1980 and high in 1984. Males were significantly heavier at birth than females and were still significantly heavier at 30 days old. Dam age significantly affected birth weight, calves from older dams being generally heavier, but had no effect on body weight at other ages.

Table 14. Mean squares from the analysis of variance to compare calves weaned at 60 days with those weaned at 120 days.

Table 15. Comparison of body weights and growth rates of early-weaned calves (W days) with calves weaned at 120 days old.

	Weight (kg) at age (days)						ADG (g) for period (days)
	n	Birth	30	60	90	120	0-30	30-60	60-90	90-120
Weaned at 120 days	318	20.4	28.5	35.5	42.8	49.7	269.1	235.2	240.6	229.9
Weaned at 60 days	35	20.2	29.0	37.0	43.6	51.3	291.9	267.5	218.4	256.2

Table 16. Mean squares from the analysis of variance for body weights of Kenana calves from birth to 180 days of age.

Mean squares at age (days)
Source of variation	d.f.	Birth	30	60	90	120	150	180
Season	2	26.2*	11.6	35.3	17.5	2.6	166.2	482.7
Year	4	34.2**	172.5***	306.1***	284.0**	191.8	111.7	78.7
Sex	1	75.2**	94.9*	67.6	69.7	139.6	135.1	29.3
Damage	8	35.4***	35.6	42.7	64.5	112.4	113.7	113.8
Error	140	7.9	19.4	34.7	62.8	105.9	129.1	153.3

Calf growth rate from birth to 180 days

Data available for this analysis were the same as those for weights to 180 days.

The mean squares from the analysis of variance of growth rate are shown in Table 18. Season had a significant effect on growth from 30 days to 60 days, 120 to 150 days and 150 to 180 days. Year of calving affected growth significantly from birth to 30 days of age only. Dam age and the sex of the calf had no significant effects on growth rate at any stage.

Least-squares means of growth rate are presented in Table 19. Growth rates from 30 to 60 days were significantly higher for calves born in the dry summer than for those born in the winter and wet summer periods. Calves born during the wet summer had significantly higher growth rates from 120 to 150 days and from 150 to 180 days of age than calves born in other seasons. Year of calving significantly affected growth rate from birth to 30 days, 1984 calves growing fastest, but had no effect on growth rate at later ages.

Growth rates declined as age advanced there being a particularly marked reduction in average daily gain (ADG) after weaning at 120 days (Figure 15).

The high ADG in the summer, from 30 to 60 days of age, was probably due to supplementary feeding of cotton stubble's and hay to these calves in this season (see Table 1). After weaning at 120 days, these calves were kept on natural grazing, this being reflected by the high ADG in wet summer from 120 to 180 days of age.

The high ADG from birth to 30 days in 1984 was probably due to the high birth weight, the calves that were heaviest at birth growing fastest (Mukhtar, 1961; Osman and Rizgalla, 1968). From Table 19, it can be seen that ADG declined as age advanced, with a sharp drop just after weaning.

Phenotypic correlations at different ages for body weight and growth rate

Table 20 shows the phenotypic correlations between body weights and growth rate from birth to 180 days of age. The negative correlations between birth weight and growth undoubtedly are a result of the fixed amounts of feed provided to calves: heavier calves have to devote more to maintenance and less to growth than their lighter-born contemporaries.

Breeding cow weights

Adult cows were not weighed regularly at Um Banein, except during 1984 and 1985, when all breeding cows on the station were weighed four times in order to establish the magnitudes of seasonal changes. The observed pattern of changes (Table 21) was similar to that already recorded for growing stock. Maximum weights were achieved following the rainy season and minimum weights at the end of the hot dry summer just prior to a rapid increase in weight at the onset of the rains.

In 1985, 46 cows and heifers within 2 weeks before parturition weighed an average of 308 kg, with post-partum weights within 2 weeks of having given birth averaging 268 kg, the loss being equivalent to 13% of body weight.

Table 17. Least-squares means of body weight for Kenana calves from birth to 180 days of age.

Variable		Weight (kg) at age
		n	Birth	30	60	90	120	150	180
Overall L.S. mean		156	20.9	29.0	36.2	43.0	49.2	53.5	56.7
Season:
	winter	79	21.7a	29.1	35.4	42.7	49.1	51.6	53.6
	dry summer	26	20.3b	29.4	37.5	43.8	49.5	53.8	57.1
	wet summer	51	20.5b	28.3	35.7	49.0	55.0	55.0	59.4
Average S.E.			0.48	0.74	0.99	1.33	1.74	1.92	2.09
Year:
	1980	10	19.2a	25.6a	32.3	39.0a	46.8	51.9	54.3
	1981	45	19.9a	27.1a	33.8	40.4a	46.6	51.8	56.1
	1982	40	21.1b	29.4b	35.9	42.6a	48.2	52.1	55.3
	1983	35	21.1ab	28.8ab	36.2	43.4a	50.3	54.3	58.4
	1984	26	22.9c	33.9c	42.9	49.3b	54.1	57.2	59.3
Average S.E.			0.62	0.97	1.30	1.75	2.28	2.51	2.74
Sex:
	female	97	20.1a	28.1a	35.5	42.2	48.2	52.4	56.2
	male	59	21.6b	29.8b	36.9	43.7	50.2	54.5	57.2
Dam age (years):
	<5	8	19.9abc	26.6	32.3	38.1	42.1	45.3	47.9
	5 - 6	23	18.1b	27.2	34.7	42.0	49.3	53.4	57.3
	6 - 7	13	20.7acd	27.5	35.5	41.6	47.1	52.7	57.0
	7 - 8	15	21.3acd	29.3	36.8	43.9	51.9	56.2	57.8
	8 - 9	13	20.9acd	29.7	37.9	44.9	52.1	54.6	57.5
	9 - 10	17	22.7d	31.0	38.7	45.7	51.6	55.6	59.4
	10 - 11	16	20.0d	28.4	35.8	43.3	49.8	55.6	59.4
	11 - 12	10	22.1acd	30.2	36.6	42.1	47.1	52.0	55.3
	>12	41	22.0ac	30.6	37.6	45.2	51.7	56.2	59.2
AverageS.E.			0.78	1.22	1.63	2.20	2.85	3.15	3.44

Within variables, means in the same column without a common superscript differ significantly (P<0.05).

Table 18. Mean squares from the analysis of variance of growth rate of Kenana calves from birth to 180 days of age.

Source of variation	d.f.	Mean square for ADG (range of days)
		0-30	30-60	60-90	90-120	120-150	150-180
Season	2	27 951.8	32 513.8*	12 079.4	7 305.6	193 270.0***	91 696.6**
Year of calving	4	61 189.5**	26 466.8*	3 152.6	25 792.3	17 900.4	25 333.8
Sex	1	1 273.6	2 521.1	12.7	13 311.9	44.2	42 573.8
Dam age	8	9 656.1	6 813.4	8 141.5	18 543.1	13 338.6	10 522.8
Error	140	12 966.2	10 589.5	15 162.2	17 917.0	18 313.2	15 434.9

* P<0.05; ** P<0.01; *'* P<0.001.

Table 19. Least-squares means of average daily gain (ADG) of Kenana calves from to 180 days of age.

Variable		n	ADG (g/day) for period
			0-30	30-60	60-90	90-120	120-150	150-180
Overall L.S. mean		156	269.7	241.9	224.6	207.5	142.0	106.5
Season:
	winter	79	245.5	211.9a	242.9	211.9	83.9a	64.7a
	dry summer	26	303.4	267.4b	212.0	189.7	140.7ab	109.8ab
	wet summer	51	260.1	246.5ab	219	220.9	201.4b	145.1b
Average S.E.			19.23	17.38	20.80	22.60	22.85	20.98
Year:
	1980	10	212.8	221.8ab	225.0	259.4	168.9	80.3
	1981	45	240.0	222.2a	220.9	205.1	173.5	141.9
	1982	40	274.7	218.5a	222.7	187.4	129.9	105.8
	1983	35	257.3	245.5a	241.5	228.2	133.4	135.1
	1984	26	363.6	301.7b	213.2	157.3	104.4	69.6
Average S.E.			25.18	22.76	27.23	29.60	29.93	31.67
Sex:
	female	97	266.5	246.4	224.3	197.3	142.6	124.8
	male	59	272.8	237.5	224.9	217.9	141.4	88.3
Average S.E.			16.01	14.47	17.32	18.83	19.04	17.47
Dam age (years):
	<5	8	224.8	188.4	192.0	134.7	105.5	85.7
	5 - 6	23	304.2	250.7	241.7	243.9	135.6	129.2
	6 - 7	13	226.5	266.1	200.9	184.5	186.7	143.8
	7 - 8	15	265.4	249.3	236.5	267.3	144.7	52.6
	8 - 9	13	293.4	270.8	235.3	238.4	83.3	95.9
	9 - 10	17	276.9	256.3	232.4	198.3	131.7	127.6
	10 - 11	16	280.9	246.3	248.3	215.5	178.6	113.2
	11 - 12	10	268.4	215.7	182.6	165.8	162.6	110.7
	>12	41	286.6	233.7	251.9	219.0	149.3	100.3
Average S.E.			31.60	28.55	34.17	37.14	37.55	34.47

Within variables, means in the same column without a common superscript differ significantly (P<0.05).

Figure 15. Average daily gain for specified periods after birth of Kenana calves at Um Banein.

Table 20. Phenotypic correlations between body weights and growth rate of Kenana calves from birth to 180 days of age.

Table 21. Seasonal variation in weight of breeding cows at Um Banein, 1984185.

Parameter		Season of weighing
		Late wet summer	End of cold winter	End of hot summer	Early wet summer
Number of cows		89	95	89	90
Mean weight	(kg)	315.4	261.9	253.1	299.4
	(s.d.)	50.3	40.0	41.5	48.1
	(range)	210-430	180-390	175-400	200-440