Effects of supplementing a low quality forage with concentrates on performance and sexual development of dairy heifers

A E El-Tayeb, T A Mohammed, A M Homeida and A A Mohammed

Department of Animal Nutrition
Institute of Animal Production
University of Khartoum
PO Box 32, Khartoum North, Sudan

ABSTRACT

A feeding trial was conducted with crossbred dairy heifers to examine the effects on animal performance and sexual development of supplementing green Sorghum bicolor with low or high levels of concentrate. Supplementation had highly significant (P<0.01) effects on average daily gain, feed conversion efficiency and heart girth of experimental animals. Animals supplemented with the high level of concentrate reached puberty significantly (P<0.05) younger and at heavier liveweight than those on the low level of concentrate. Heifers fed forage only did not reach puberty during the experimental period.

RESUME

Performances et développement sexuel de génisses de race laitière alimentées avec un fourrage de qualité médiocre complémenté avec des concentrés

Un essai d'alimentation a été effectué sur des génisses métisses de race laitière pour examiner l'effet sur leurs performances et leur développement sexuel, de la complémentation de fourrage vert de Sorghum bicolor avec deux niveaux de concentrés. La complémentation avait un effet hautement significatif (P<0,01) sur les gains moyens quotidiens, le taux de conversion des aliments et le périmètre thoracique des animaux. Les génisses recevant le niveau élevé de concentrés avaient atteint la puberté à un âge significativement (P<0,05) inférieur et à un poids vif supérieur à celui des sujets soumis au faible niveau de concentré. Enfin, aucune des génisses recevant uniquement du fourrage n'avait atteint la puberté au cours de la période expérimentale.

INTRODUCTION

Sorghum bicolor is a popular ruminant feed in Sudan. However, because its digestible crude-protein content is low, animals fed only this forage do riot perform well. Supplementing forage-based diets with concentrates can improve rumen fermentation, fibre digestibility and forage intake (Church and Santos, 1981; Lee et al, 1985; McCollum and Galyean, 1985). El-Tayeb and Gaber (1987) demonstrated that supplementing a combination of forages with concentrates improves performance and reproductive traits of Sudanese crossbred dairy heifers However, during much of the year only one forage may be available. Therefore, the objective of this research was to examine the performance and sexual development of dairy heifers fed a low-quality forage (Sorghum bicolor) supplemented with a concentrate mixture.

MATERIAL AND METHODS

Eighteen crossbred (Butane x Friesian) dairy heifers (average liveweight approximately 100 kg) were used in this trial; they were selected at random from a large herd which was housed and treated as one group. The animals were allowed a seven-day adaptation period after which they were stratified according to liveweights into three similar groups, of six animals each, which were then randomly assigned to one to the following treatments:

· forage only (diet A)
· forage plus 1 kg concentrate mixture (diet B)
· forage plus 2 kg concentrate mixture (diet C).

Heifers were penned and fed in pairs.

The concentrate mixture comprised 35% sorghum grain, 35% sunflower cake, 27% wheat bran, 2% limestone flour and 1% common salt.

For the first 130 days of the trial Sorghum bicolor was the only forage offered to the experimental animals. For the next 45 days sorghum was in short supply and the heifers were fed a mixture of groundnut hulls, alfalfa and sorghum. Sorghum then became freely available again and was offered to the heifers until they reached puberty.

The chemical analysis of the feed ingredients is shown in Table 1.

The concentrate was offered to the heifers once a day at 0800 hours throughout the experimental period. The heifers ate all the concentrate offered. Clean water was available throughout the experimental period in all pens.

The daily allowance of the forage was offered in one meal at 1000 hours, the amount offered being adjusted daily until the refusals were about 10% of-the amount offered. Forage refusals were collected the following morning and the weight recorded. The daily feed intake was then calculated by subtracting the refusals from the amounts offered.

The heifers were weighed, and their heart girths measured, every two weeks at 0700 hours before the morning meal. Average daily gain of the heifers was calculated by dividing the average biweekly liveweight gain by 14. Feed conversion ratio (kg feed/kg weight gain) was also computed.

Table 1. Chemical composition of ingredients of treatment diets

	Composition (% DM)
	Concentrate mixture	Sorghum bicolor	Groundnut hulls	Alfalfa
Dry matter (DM)	98.4	94.3	97.0	93.6
Ash	6.2	8.2	6.5	10.6
Crude protein (CP)	20.8	4.1	5.8	16.8
Crude fibre (CF)	33.4	39.3	66.5	28.0
Ether extract (EE)	6.3	1.8	2.7	2.1
Nitrogen-free extract (NFE)	31.5	45.0	18.4	36.1
ME, MJ/kg DM	10.52	9.31	7.43	9.12

Chemical compositions were determined by methods described by AOAC (1980)
Metabolisable energy (ME) values were obtained using the following equation (Ellis, 1980):
ME (MI/kg DM) = 0.012CP + 0.031EE + 0.005CF + 0.014NFE

Sexual maturity was detected by the first presence of progesterone in the peripheral blood of the heifers. Jugular venous blood (5 ml) was obtained from each heifer once a week during the experimental period, by direct venipuncture using 22G needles. Serum progesterone was assayed by direct solid-phase radioimmunoassay.

Data were subjected to analysis of variance applicable to the randomised complete-block design (Steel and Torrie, 1980). Differences among treatment means were determined by least significant differences (Steel and Torrie, 1980).

RESULTS AND DISCUSSION

There were no significant differences (P>0.05) in dry-matter intake across treatments (Table 2). This finding agrees with that of Tayler and Wilkison (1972), but contradicts other studies which indicated that roughage intakes were depressed by increasing the level of concentrate supplementation (McCullough, 1970; Leaver, 1973).

As expected, metabolisable energy and crude-protein intakes increased (P<0.01) as the level of concentrate supplement was increased (Table 2).

There were highly significant (P<0.01) differences in the final liveweights, average daily gains and feed conversion ratios of heifers in the three treatment groups (Table 3). The weight improvement in heifers fed concentrates was expected, as the concentrate would provide nutrients which may be lacking or deficient in the forage. Previous studies (Tayler and Wilkison, 1972; Leaver, 1973; El-Tayeb and Gaber, 1987) also found that liveweight gain increased as the rate of concentrate supplementation increased. The feed conversion ratios found in the present study were higher than those observed by El-Tayeb and Gaber (1987); this discrepancy may be due to the roughage used, which directly affects the dry-matter intake and hence feed conversion ratio.

Table 2. Effect of concentrate supplements on feed intake of dairy heifers over 130 days

		Diet A	Diet B	Diet C
Dry-matter intake (kg)
	Sorghum	3.33	3.17	3.02
	Concentrate	-	0.98	1.96
	Total	3.33	4.15	4.98
Daily dry-matter intake (% of liveweight)		2.52	2.59	2.55
Daily ME intake (MJ)		31.00a	39.83b	48.73c
Daily crude-protein intake (kg)		0.14a	0.33b	0.52c

Means in the same row followed by a different letter differ significantly (P<0.01)

Table 3. Effect of concentrate supplements on liveweight gain and feed efficiency of dairy heifers over 130 days

	Diet A	Diet B	Diet C
Initial liveweight (kg)	100.0	99.8	100.2
Final liveweight (kg)	119.8a	160.8b	195.7c
Average daily gain (kg)	0.15a	0.47b	0.74c
Feed conversion ratio (kg feed/kg weight gain)	19.8a	8.9b	6.8c

Means in the same row followed by a different letter differ significantly (P<0.01)

The relationship between liveweight and heart girth is shown in Table 4. The greater (P<0.01) increase in heart girth was achieved by animals on the high level of supplementation. Shioya et al (1975) and Takla (1988) also found that concentrate supplementation had a highly significant effect on heart girth.

Serum progesterone was not detected in heifers in group A (the unsupplemented heifers), or in two heifers in group B. Serum progesterone concentrations of the remaining heifers are shown in Table 5. These data are in line with those reported by Donaldson el al (1970) who found that the plasma progesterone concentrations of heifers ranged from 0.3 to 3.9 ng/ml when the first sample was obtained.

Ovary surface examination by rectal palpation showed that high concentrations of progesterone were accompanied by the presence of corpus luteum. This agrees with previous work by Rakha et al (1970).

Table 4. Effect of concentrate supplements on body conformation of dairy heifers

	Diet A	Diet B	Diet C
Initial
Liveweight (kg)	100.0	99.8	100.2
Heart girth (cm)	112	112	111
Correlation coefficient	0.99	0.99	0.97
Final
Liveweight (kg)	119.8a	160.8b	195.7c
Heart girth (cm)	136a	187b	219c
Correlation coefficient	0.98	0.98	0.97

Means in the same row followed by a different letter differ significantly (P<0.01)

Table 5. Serum progesterone concentration of dairy heifers ^a

	Serum progesterone concentration (ng/ml) for individual heifers
	Diet B				Diet C
1st Ds	0.77	2.78	0.94	2.21	0.89	2.21	3.35	1.08	0.87	0.94
2nd Ds	1.89	0.40	3.92	0.48	1.75	0.48	0.54	1.98	1.53	3.40
3rd Ds	3.21	0.98	0.44	0.64	3.45	0.64	ND	3.47	2.20	ND
4th Ds	0.42	3.12	0.82	1.74	ND	1.74	ND	0.67	0.60	0.91
5th Ds	0.69	ND	1.68	3.27	0.98	3.27	0.69	1.20	0.93	1.63

^a All heifers in group A, and two heifers in group B. did not reach puberty
Ds = Detectable sample
ND = Non-detectable

Some heifers showed visible signs of oestrus before progesterone was detected in their peripheral blood.

Heifers fed the high level of concentrate reached puberty (first onset of oestrus) at a significantly (P<0.05) younger age (20.5 months) and heavier liveweight (248 kg) than heifers fed the low level of concentrate (23.9 months and 231 kg, respectively). Generally, these findings agree with those of previous studies (Rakha et al, 1970; Short and Bellows, 1971; Little and Kay, 1979; Stewart et al, 1980; El-Tayeb and Gaber, 1987) which showed that the improved nutrition affected the onset of puberty in cattle.

The relationship between age and liveweight at puberty (r = 0.33) was positive, but not significant (P>0.05), indicating that animals reached puberty at a given liveweight rather than at a given age.

CONCLUSIONS

This work demonstrates that supplementing poor quality forage improves the performance and reproductive traits of crossbred dairy heifers. More research is needed to examine the influence of different types of supplement and combinations of forages, and to determine the optimum level of supplementation.

REFERENCES

AOAC (Association of Official Analytical Chemists). 1980. Official method of analysis. 13th edition. AOAC, Washington, DC, USA. 1018 pp.

Church D C and Santos A. 1981. Effect of graded levels of soybean meal and of a nonprotein nitrogen-molasses supplement on consumption and digestibility of wheat straw. Journal of Animal Science 53:1609-1615.

Donaldson L E, Basset J M and Thorburn G D. 1970. Peripheral plasma progesterone concentration of cows during puberty, oestrous cycle, pregnancy and lactation and the effect of undernutrition or exogenous oxytocin on progesterone concentration Journal of Endocrinology 48:599.

Ellis N. 1980. The nutrient composition of Sudanese animal feeds Bull 1. Northern and Central Sudan. Animal Nutrition Research Laboratory, Kuku, Khartoum North. Appendix 1, p. 19.

El-Tayeb A E and Gaber S S. 1987. Effects of concentrate supplements to forages on some production traits of dairy heifers. Sudan Journal of Veterinary Science and Animal Husbandry 27:70-77.

Leaver J D. 1973. Rearing of dairy cattle. 4. Effect of concentrate supplementation on the live weight gain and food intake of calves offered roughages ad libitum. Animal Production 17:43-52.

Lee G L, Hennessy D W. Williamson P J. Nolan J V, Kempton R J and Leng R A. 1985. Responses to protein meal supplements by lactating beef cattle given a low quality pasture hay. Australian Journal of Agricultural Research 36:729.

Little W and Kay R M. 1979. The effect of rapid rearing and early calving on the subsequent performance of heifers. Animal Production 29:131-142.

McCollum F T and Galyean M L. 1985. Influence of cottonseed meal supplementation on voluntary intake, rumen fermentation and rate of passage. Journal of Animal Science 60:570-577.

McCullough T A. 1970. A study of the effect of supplementing a concentrate diet with roughages of different quality on performance of Friesian steers. Journal of Agricultural Science, Cambridge 75:327-335.

Rakha A M, Hale D and Igboeli G. 1970. The age at puberty in local breeds of cattle in Central Africa. Journal of Reproduction and Fertility 22:369.

Shioya Y. Obata T and Fukuhara R. 1975. Growth and growth patterns of Japanese cattle on pasture. 3. Relationship of body measurements with body-weight in growing female calves. Animal Breeding Abstracts 43:448.

Short R E and Bellows R A. 1971. Relationships among weight gains, age at puberty and reproductive performance in heifers. Journal of Animal Science 32: 127-131.

Steel R G D and Torrie J H. 1980. Principles and procedures of statistics. A biometrical approach. 2nd edition. McGraw-Hill, New York, USA. 633 pp.

Stewart T S. Long C R and Cartwright T C. 1980. Characterization of cattle of a five-breed diallel. 3 Puberty in bulls and heifers. Journal of Animal Science 50:808.

Takla A G. 1988. Effect of level of feeding Holstein-Friesian heifers in late pregnancy on first lactation performance. MSc Thesis. University of Khartoum, Khartoum, Sudan. pp. 35-46.

Tayler J C and Wilkison J M. 1972. The influence of level of concentrate feeding on the voluntary intake of grass and on live weight gain by cattle. Animal Production 14:85-96.