Animal Sciences Research and Reviews

Special Circular 156

Effects of Age at Weaning and Diet on Growth of Calves

Summary

This experiment was conducted to determine the effects of diet on calves weaned at either 100 days of age (early-weaned) or 205 days of age (normal-weaned). Early-weaned calves had a greater (P < 0.001) average daily gain (ADG) than normal-weaned calves from 100 to 205 days of age. This resulted in early-weaned calves having heavier (P < 0.01) weights at 205 days of age if fed either 100% or 90% concentrate diets compared with normal-weaned calves. Creep-feeding normal-weaned calves did not result in increased weights at 205 days of age (P > 0.10). Early-weaned calves fed either 90% or 100% concentrate diets had greater (P < 0.001) backfat at 205 days of age with no difference (P > 0.10) in the Longissimus dorsi area compared with early-weaned calves fed a 60% concentrate diet. At slaughter, early-weaned calves had a higher (P < 0.05) quality grade than normal-weaned calves. Backfat, ribeye area, dressing percentage, and yield grade were not affected (P > 0.10) by age at weaning or diet prior to 205 days of age.

Introduction

In many parts of the United States, calves are born in the spring and sold as feeder calves the following October or November. In the midwest, as in many other parts of the country, land is an economically limiting factor to cow herd numbers. In many years, dry, hot weather in July, August, and September causes pasture growth to slow, and producers are forced to either feed hay and grain to their cow herd or accept reduced weaning weights. If the winter supply of feed is fed during the summer, the economic loss can be devastating due to reduced calf weaning, sale weights, and the need to purchase winter feed for the cow herd. Early-weaning calves may be an economically advantageous solution to limited feed supplies. Peterson et al. (1987) reported that early-weaned cow-calf pairs were 43% more efficient in converting total digestible nutrients into calf gain than were normal-weaned cow-calf pairs. Furthermore, Houghton et al. (1990) reported that early-weaning calves at approximately 30 days of age reduced postpartum anestrous interval by 24 days compared to normal-weaned controls.

Creep feeding has been used in many instances, but it has several drawbacks: creep feeders must be purchased, creep feeders must be moved from pasture to pasture, feed must be taken to the feeders often, and cows damage the feeders trying to get to the grain. However, the biggest disadvantages are the following: creep feeding does not improve cow condition score going into the winter because the calf is still nursing the cow, and creep-fed calves often are discounted by feedlot order buyers because they carry too much fat when they enter the feedlot. It is more nutritionally efficient to feed a calf to gain weight than it is to feed the mother in hope of increasing milk production, which would increase the gain of the calves. Furthermore, after approximately 100 days of age, the growth rate of calves is limited by the amount of protein and energy in the cows' milk and available pasture.

The objectives of this experiment were to determine 1) the effects of age at weaning (100 vs 205 days) and nutritional regimen on performance, 2) the effects of creep feeding calves during the months of August and September, and 3) the effects of diet prior to 205 days of age on finishing period steer performance and carcass characteristics.

Experimental Procedures

One-hundred-twenty cow-calf pairs were allotted to either early-weaned or normal-weaned groups. Sixty-eight early-weaned calves were transported by truck from the Jackson Branch of OARDC to the OARDC feedlot in Wooster, Ohio, on June 23, 1995. Upon arrival, the calves received a 20% protein receiving diet for the first 18 days. On July 11, the calves were allotted by weight and sex to the four dietary treatment groups (17 calves per treatment) and penned individually with access to their own feed bunk and water cup. Therefore, each calf was an experimental unit. The four dietary treatment groups were 1) a 100% concentrate diet formulated to contain 12% crude protein (100% concentrate, 12% CP), 2) a 100% concentrate diet formulated to contain 16% crude protein (100% concentrate, 16% CP), 3) a 90% concentrate diet formulated to contain 16% crude protein, using peanut hulls as the source of fiber at 10% of the diet (90% concentrate, 16% CP), and 4) a 60% concentrate diet formulated to contain 16% crude protein (60% concentrate, 16% CP). For all diets, the concentrate portion of the diet consisted primarily of whole shelled corn and soybean meal. Pen construction consisted of metal gates and a slatted concrete floor, and pens were located in a totally enclosed barn. All steers were fed once daily beginning at 0800 hours, and feed refusals were recorded daily for each steer. Initial and final weights were determined using average weights from two consecutive days by weighing each animal prior to feeding. Interim weights were determined every 28 days. The ADG, dry matter intake (DMI), and feed efficiency (gain/feed) were determined for each 28-day period, as well as for the total trial. The early-weaning portion of the trial ended on October 3, 1995 (84-day trial). Feed samples were collected every 7 days throughout the trial. Monthly composites of feed were analyzed for dry matter (DM) (Goering and Van Soest, 1970), and nitrogen (N) content was determined by macro-Kjeldahl (AOAC, 1984). Neutral detergent fiber (NDF) was determined according to the procedures of Van Soest et al. (1991).

Normal-weaned calves remained with their dams throughout the summer. On August 3, 1995, the cow-calf pairs were divided into two groups based on cow production level and calf weight to determine the effects of creep feeding during the final 60 days prior to weaning. The dietary treatments consisted of 1) a 60% concentrate complete pellet formulated to contain 16% CP and 2) a non-creep fed control. Individual calf performance was determined every 28 days. Feed analysis was conducted according to the procedures previously described.

On October 3, 1995, the normal-weaned steers were transported from the OARDC Jackson Branch to the OARDC beef feedlot in Wooster, Ohio. The steers remained in the same treatment groups to which they were assigned during the summer and were fed a 90% concentrate, 14% CP diet until they reached an average weight of 900 pounds. The steers then were switched to a 90% concentrate, 12.5% CP diet until they reached slaughter weight (target weight 1175 pounds). From 205 days of age until the termination of the experiment, the steers were fed in pens containing 9 to 10 animals per pen. Steers were removed from the trial on an individual basis when they reached 1175 pounds. Carcass data were obtained from each animal to determine if age at weaning or nutritional strategy prior to 205 days of age had any effects on carcass characteristics.

Data were analyzed using analysis of variance procedures for a completely randomized, split-plot design experiment using the general linear model procedure of SAS (SAS, 1988). Weaning status served as the whole plot, and dietary treatment served as the sub-plot. For the early-weaned calves, each calf served as an experimental unit. For the normal-weaned calves, each calf served as an experimental unit for gain data. Intake data were not analyzed statistically, because individual calf intakes could not be determined on pasture.

Backfat and loin-eye measurements were determined by ultrasound on the early-weaned calves at the initiation of the trial and during the first week of October to help determine the composition of gain of the animals prior to 205 days of age. Ultrasound information could not be determined on the normal-weaned calves due to the lack of an adequately grounded electrical source at the farm.

Results and Discussion

Effects of diet and creep status on weight and ADG of calves from 100 to 205 days of age are shown in Table 1. Early-weaned calves that were fed either 100% or 90% concentrate diets had heavier (P < 0.01) weights at 205 days of age and greater (P < 0.001) ADG from 100 to 205 days of age compared with normal-weaned calves. Early-weaned calves fed a 60% concentrate diet were intermediate in 205-day weight and ADG. The effects of diet on early-weaned calf performance from 100 to 205 days of age are shown in Table 2. Early-weaned calves fed either 100% or 90% concentrate diets had greater overall ADG (P < 0.01) and feed efficiency (P < 0.001) compared with calves fed 60% concentrate diets. There were no differences (P > 0.10) in either DMI or 205-day hip height due to diet. Furthermore, there were no differences in performance (P > 0.10) between calves fed the 100% concentrate diet containing 12% CP and those fed the 100% concentrate diet containing 16% CP. In general, the calves consumed the high-concentrate diets without any detected nutritional disorders from 100 to 205 days of age and with very good conversions of feed to gain. Harvey and Burns (1988a,b) also reported that early-weaned calves were very efficient in their use of concentrate feed for gain.

The effects of diet on changes in backfat and the L. dorsi area of early-weaned calves from 100 to 205 days of age are shown in Table 3. Calves fed the 100% and 90% concentrate diets had a greater (P < 0.001) 205-day backfat thickness and rate of backfat accretion compared with calves fed the 60% concentrate diet. There were no differences (P > 0.10) in the 205-day L. dorsi area due to diet. Therefore, increasing dietary energy density from 60% to 100% concentrate resulted, in part, in an increase in fat accumulation.

The effects of diet and weaning status on finishing period steer performance and carcass characteristics are shown in Table 4. There were no differences (P > 0.10) in finishing period performance due to diet prior to 205 days of age. However, some early-weaned steers stopped growing late in the finishing period. Twenty percent of the steers fed the 100% concentrate, 12% CP diet failed to reach 1050 pounds compared with no steers fed the 60% concentrate diet or weaned at 205 days of age that failed to reach 1050 pounds. This may be a practical indication that early-weaning calves onto a 100% concentrate diet may cause problems late in the feeding period. The only difference in carcass characteristics was that the steers fed the 90% concentrate, 16% CP diet had a higher (P < 0.05)

quality grade compared with calves weaned at 205 days of age. However, steers fed the 100% concentrate, 12% CP diet and the 100% concentrate, 16% CP diet had 0.71 and 0.69 inches of backfat and a calculated yield grade of 4.2 and 4.2, respectively. These backfat and yield grade values may be unacceptable to many segments of the beef industry compared with the early-weaned calves fed the 60% concentrate diet and the calves weaned at 205 days of age. Quite possibly, a relatively aggressive implant strategy may be warranted with early-weaned calves fed high-concentrate diets. Frame size and genetics should be further analyzed to determine cattle that are best suited for early-weaning on high concentrate diets. The choice of the most appropriate early-weaning diet should be based on the calf producer's feed costs and most critical marketing criteria. The most important marketing criteria may change depending on whether calves are being marketed at 205 days of age or retained throughout the feeding period.

Table 1. Effects of diet and creep status on weight and average daily gain (ADG) of calves from 100 to 205 days of age.
	Early-weaned					Normal-weaned
Item	100% Conc. 12% CP	100% Conc. 16% CP	90% Conc. 16% CP	60% Conc. 16% CP		Not creep-fed	Creep-fed	SEM1
Initial weight, pounds	328.0	317.0	314.0	318.0		340.0	335.0	14.65
Final weight, pounds	610.0a	605.0a	611.0a	569.0ab		541.0b	558.0b	18.77
ADG2, pounds/day	2.76c	2.82c	2.90c	2.47d		1.98e	2.18e	0.10
1 SEM = Standard error of mean. 2 ADG = Average daily gain. ab Means within a row with different superscripts differ (P < 0.01). cde Means within a row with different superscripts differ (P < 0.001).

Table 2. Effects of diet on early-weaned calves from 100 to 205 days of age.
Item1	100% Conc. 12% CP	100% Conc. 16% CP	90% Conc. 16% CP	60% Conc. 16% CP	SEM2
Number of calves	17	17	17	17
Weaning weight, pounds	328.30	317.32	314.47	317.50	15.27
Initial weight, pounds	362.21	358.63	360.88	359.48	16.82
Final weight, pounds	609.58	604.63	611.14	569.43	19.57
Hip height, inches	43.89	43.92	44.43	43.87	0.46
BCS	6.4	6.2	6.3	5.9	0.17
Period 1 ADG, pounds/day	2.93a	2.96a	2.75a	1.99b	0.15
Period 2 ADG, pounds/day	2.88	2.94	2.86	2.44	0.14
Period 3 ADG, pounds/day	3.02	2.88	3.33	3.07	0.23
Overall ADG, pounds/day	2.94c	2.93c	2.98c	2.50d	0.11
Period 1 DMI, pounds/day	10.38	10.08	10.39	10.21	0.45
Period 2 DMI, pounds/day	12.67	11.90	12.63	13.14	0.51
Period 3 DMI, pounds/day	14.48	13.90	15.14	15.94	0.64
Overall DMI, pounds/day	12.51	11.96	12.72	13.09	0.49
Period 1 G/F, pound/pound	0.284a	0.297a	0.267a	0.195b	0.013
Period 2 G/F, pound/pound	0.230c	0.251c	0.228c	0.186d	0.012
Period 3 G/F, pound/pound	0.211	0.208	0.210	0 .195	0.016
Overall G/F, pound/pound	0.238a	0.248a	0.234a	0.192b	0.008
1 BCS = Body condition score, ADG = average daily gain, DMI = dry matter intake, and G/F = gain/feed. 2 SEM = Standard error of mean. ab Means within a row with different superscripts differ (P < 0.001). cd Means within a row with different superscripts differ (P < 0.01)

Table 3. Effects of diet on early-weaned calves backfat and ribeye area from 100 to 205 days of age.
Item	100% Conc. 12% CP	100% Conc. 16% CP	90% Conc. 16% CP	60% Conc. 16% CP	SEM1
On-test back fat, inch	0.09	0.08	0.09	0.09	0.01
Off-test backfat, inch	0.27a	0.27a	0.26a	0.16b	0.02
Backfat change, inch	0.18a	0.19a	0.17a	0.08b	0.02
On-test L. dorsi area, inch2	5.48	5.53	5.55	5.48	0.20
Off-test L. dorsi area, inch2	7.45	7.61	7.55	7.15	0.19
L. dorsi area change, inch2	1.97	2.08	2.00	1.67	0.16
1 SEM = Standard error of mean. ab Means within a row with different superscripts differ (P < 0.001).

Table 4. Effects of diet and creep status on steer performance during the finishing period, and carcass characteristics.
	Early-weaned					Normal-weaned
Item	100% Conc. 12% CP	100% Conc. 16% CP	90% Conc. 16% CP	60% Conc. 16% CP		Not creep-fed	Creep-fed	SEM1
Weight on test, pounds	634	622	638	567		577	581	25.8
Weight off test, pounds	1163	1158	1155	1168		1168	1165	13.6
ADG2, pounds/day	2.84	2.78	2.86	3.19		3.11	3.04	0.16
Days on test	187	198	186	192		191	196	0.13
Hip height off test, inches	50.1	50.0	50.4	50.8		50.6	51.0	0.44
DMI3, pounds/day	16.4	16.6	17.1	17.7		16.9	17.5	. . .
G/F4, pound/pound	0.173	0.167	0.167	0.180		0.184	0.179	. . .
% not reaching 1050	20.0	12.5	10.0	0.0		0.0	0.0	9.2
Hot carcass weight, pounds	722	701	700	711		723	705	12.42
Dressing %	62.1	60.5	60.6	60.9		61.9	60.5	0.76
Backfat, inch	0.71	0.69	0.62	0.54		0.54	0.51	0.07
% KPH5	3.6	3.6	3.6	3.4		3.6	3.5	0.11
L. dorsi area, inch2	12.3	11.5	12.0	13.3		13.5	12.8	0.22
Quality grade6	4.3ab	3.7ab	4.6a	4.3ab		3.5b	3.4b	0.34
Yield grade	4.2	4.2	3.9	3.5		3.6	3.5	0.26
1 SEM = Standard error of mean. 2 ADG = Average daily gain. 3 DMI = Dry matter intake. 4 G/F = Gain/feed. 5 KPH = Kidney, pelvic fat, and heart. 6 Quality grade: 1 = low select, 2 = high select, 3 = low choice, 4 = average choice, and 5 = high choice. ab Means within a row with different superscripts differ (P < 0.05).

References

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Houghton, P.L., R.P. Lemenager, L.A. Horstman, K.S. Hendrix, and G.E. Moss. 1990. Effects of body composition, pre- and postpartum energy level and early weaning on reproductive performance of beef cows and preweaning calf gain. J. Anim. Sci. 68:1438.

Peterson, G.A., T.B. Turner, K.M. Irvin, M.E. Davis, H.W. Newland, and W.R. Harvey. 1987. Cow and calf performance and economic considerations of early weaning of fall-born beef calves. J. Anim. Sci. 64:15.

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Van Soest, P.J., J.B. Robertson, and B.A. Lewis. 1991. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74:3583.