Milk production level and calf-rearing system affecting Boran, Ethiopian zebu cattle breed, cow-calf performance

Z Yilma, Y Gojjam and M Shumye

Dairy Technology, Ethiopian Agricultural Research Organization, Holetta Agricultural Research Center, P.O. Box 31, Holetta, Ethiopia
zeyilmak@yahoo.fr

Abstract

Milk yield, reproductive performance, dry matter intake, milk composition and calf growth were studied for Boran (Ethiopian zebu breed) cows under different milk production levels and calf rearing methods. 39 Boran cows in their 2^nd and 3^rd parities were used for the study in a 2 x 2 factorial arrangement with main factors being suckling (partial suckling Vs non-suckling) and milk yield (low- and high-yielding).

Suckling has resulted in increased total milk yield as compared to non-suckling in both milk yield groups: 793 Vs 369 kg for low-yielders and 1142 Vs 819 kg for high-yielders. Suckling and high-yielding cows consumed 0.6 kg and 0.8 kg more concentrate and total dry matter daily than non-suckling and low-yielding cows, respectively. Non-suckling and high-yielding cows produced 52 kg and 31 kg, respectively more hand-milked milk monthly (P<0.05) than suckling and low yielding cows. Although partial suckling resulted in reduced fat percentage in milk obtained through hand milking, total milk yield was increased. Partial suckling, however, prolonged calving to first heat, days open and cycling compared with non-suckling. Suckling also resulted in higher (P<0.01) average daily weight gain to weaning.

Smallholder dairy enterprises in Ethiopia that are based on local cows need to consider the importance of suckling for increased productivity of the farm particularly in terms of milk yield and calf growth rate. As suckling resulted in increased milk yield, this practice should be accompanied by improved feeding. Further studies are needed in this line to address the economic implications of such practice. The need for similar studies under different production systems is also imperative to determine and implement the most appropriate strategy to improve overall life time productivity of local cows that include reproduction traits, milk production, calf growth and survival with suckling practices.

Key-words: Boran, feed intake, growth, milk production, partial-suckling, reproduction

Introduction

Indigenous cows, which are generally low milk producers, are the major sources of milk in Africa. In Ethiopia they account for 97% of the country's annual milk production (Tedla et al 1991). Research findings (EIAR 1976) on Ethiopian indigenous cattle breeds indicated that milk yield ranged between 500 and 700 litters in less than 100 days of lactation period, under average to good management conditions in the Ethiopian context. Even under a research center management condition, average milk yield didn't exceed 500 liters and lactation length was about 150 days (Kebede 1984; Mukasa-Mugerwa 1989; Yilma 1999).

Boran (Ethiopian zebu breed) performance evaluation at Holetta Research Center showed high variability in milk yield and lactation length that ranged from 1 to 1800 kg and 3 to 300 days, respectively under hand milking condition (Gojjam et al 2002). The low milk yields and short lactation length observed under this condition might not reflect the true genetic potential of the animal. This is evident because the low yield reported under hand milking in this study is not sufficient to successfully foster growth of a calf to weaning age, whereas cows normally support their calves to this age under suckling condition. Therefore, the low yield might be attributed to the milk let down character of indigenous cows when milked in the absence of their calves. Earlier reports by Tegegne et al (1994) and Little et al (1989) revealed that indigenous cows produced significantly more milk for their calves and human consumption under partial suckling and hand milking method. This system, however, increased days from calving to conception (Tegegne et al 1994). Partial suckling has also been reported to increase milk yield and lactation length of Horro cows (Kumsa and Gebre-Yohannes 1995).

On the other hand, milk fat and protein make milk an economic and nutritionally important asset. The composition of milk varies due to a number of factors including breed, age, feed, disease and stage of lactation. Milking technique may have a profound effect on fat content and thus on total solids content because incomplete milking may leave a considerable volume of fat-rich milk in the udder (McDonald et al 1995).

However, none of the earlier studies showed how local cows with high variability of milk yield potential respond to suckling stimulation in terms of milk yield and reproductive performance. Information in milk composition, dry matter intake (DMI) and calf growth rate of local cows in general and Boran cows in particular is lacking.

This paper reports results of milk composition, DMI, milk production and reproductive performance of Boran cows and pre-weaning growth rate of their calves under different production levels and suckling conditions.

Materials and Methods

Study area

The study was carried out at Holetta Agricultural Research Center (altitude: 2400masl; annual rainfall: 1100mm; average temperature minimum: 6°C, maximum: 24°C) located 45km west of Addis Ababa, Ethiopia (3°24'N to 14°53'N and 33°00'E to 48°00'E). The study area experiences two major seasons, the wet (June to September) and the dry (October to May).

Animals and treatments

A total of 39 multiparous (2^nd and 3^rd parity) Boran cows from Holetta Agricultural Research Center Dairy Cattle Research Program were used in this study. Cows were inseminated using pure Holstein semen to produce first filial (F1) calves. Cows were grouped in a 2 x 2 (2 suckling groups x 2 milk yield groups) factorial arrangement. Partial suckling (S) and non-suckling (NS) (milking without calf suckling) methods were tested to compare the milk yield and reproductive performance of Boran cows and growth rate of their calves. The cows were allocated into two groups under each suckling group based on parity and previous milk production: 1) low-yielding (LY) - cows producing milk lower than the average yield of over 100 Boran cows at the center (675kg/lactation) and 2) high-yielding (HY) - cows producing higher than the average (Table 1).

All cows were drenched and sprayed against internal and external parasites, respectively before the commencement of the experiment. The cows were stall fed with natural pasture hay ad libitum. A concentrate mixture composed of wheat middling (32%), wheat bran (32%), noug (Guizocia abyssinica) cake (34%), bone meal (1%) and salt (1%) was supplemented at a rate of 0.5 kg for every kg of milk produced daily during milking. The mixture had 81.0% DM, 29.5% crude protein, 46.9% neutral detergent fiber and 71.8% digestible organic matter. A kilogram of concentrate in excess of the allowance was given to all cows for anticipated increase in milk yield. Feed refusals were measured before next feeding and intakes were calculated by subtracting refusals from that offered. The cows had free access to clean water all the time. During the experimental period two bucket fed female calves died during the first two weeks of their life, therefore data were not available for them.

Experimental procedure and measurements

Partial-Suckling (S)

Calves had free access to suckle their dams for the first 4 days to ensure that they got enough colustrum. They were then separated from their dams and kept in individual boxes until weaning at 90 days of age. Calves were allowed to suckle their respective dams for 2 min before each of the two daily milkings to stimulate milk let down. They were then tied in front of their dams while cows were hand-milked. After milking, calves were allowed to resuckle their respective dams for 30 minute. Calf milk consumption was estimated by the weigh-suckle-weigh technique (Beal et al 1990) using a balance (100 g sensitivity) at each milking. The daily milk yield for this group was obtained by adding the estimated milk consumed by the calf and milk off-take by hand milking.

Non-Suckling (NS)

Calves were separated from their dams right at birth and kept in individual boxes until weaning at 90 days of age. During the first 4 days, they consumed 24 L of colustrum (3 L per day, 1.5 L in the morning and 1.5 L in the evening) by bucket-feeding. They were then fed on bucket following the center's procedure (260 kg of whole milk in 98 days) (unpublished data). Milk yield of cows was measured and recorded two times per day during AM and PM milkings.

Reproductive management and live weight measurement

A teaser bull was run with the cows for heat detection twice a day (in the morning and in the evening) for one hour each time. Cows detected in heat were served by artificial insemination. Cows with repeated heat were served up to four times. Cows not in heat after service were diagnosed for pregnancy 45 days after service. Live weight of cows and calves were taken every second week.

Laboratory analysis of milk composition

During the experimental period, a total of 541 fresh milk samples were collected fortnightly from experimental cows from morning and evening milkings. Composite morning and evening milk samples were kept overnight in a refrigerator maintained below 4 ^oC before undertaking the required test for chemical composition. Milk fat analysis was run using the Gerber method (BSI 1989). Protein content was determined using the formaldehyde titration method according to the technique described by Pyne (1932). Total solids (TS) were determined by oven drying 5g of milk (Marth 1978). Though not reported, all tests were also made using a computer based lactometer (Delta Instruments 2000). Monthly milk yield obtained through hand-milking was considered to render comparison of the evolution of milk chemical composition and milk yield possible.

Statistical Analysis

Data collected on milk yield, reproductive performance, DMI and milk compositions (% fat, % protein and % total solids) were subjected to statistical analysis using the General Linear Model (GLM) procedure of the Statistical Analysis System (SAS 2001). The independent variables considered for this study include: suckling group, milk yield group, parity, calving year and calving season. Means were separated using the Least Significant Difference (LSD) method. Experimental cows calved between 2001 and 2002 and calving year was considered as an independent variable for the estimation of monthly milk yield and milk composition in the original analysis. However, as it didn't have any apparent effect it was excluded from the model and the analysis was rerun.

Results and discussion

Although S cows yielded 342 kg less hand-milked milk (HMM) than NS cows, S resulted in 373 kg increase in total milk. NS*HY cows produced the highest HMM followed by NS*LY, S*HY and then S*LY cows (Table 2). Within LY, however, 288 kg more milk was hand-milked from NS cows as compared to those in S group. For HY this difference was much higher amounting to 497 kg though the percent increment was similar (154%) Suckled milk on the other hand amounted to 612 and 820 kg for LY and HY, respectively (Table 2).

The holding-up of milk is more pronounced with LY than HY within the suckling cows. This could be attributed to the instinct that low-yielders might be endowed to reserve the low amount of milk secreted to satisfy the need of their own calves through suckling. This agrees with the explanation given by Barret and Larkin (1974) cited by Kumsa and Gebre-Yohannes (1995) that the strong maternal instinct of indigenous cows to have influence on milk let down, which is expressed by unwillingness to let down milk into buckets, preferring to hold it back for the calf. Another explanation could be that low yielding cows require a high oxytocin level to press milk out of an incompletely filled alveolus (Bruckmaier 2001). This was evidenced by the observation of the present study where HY cows produced 78 % more HMM than the LY ones. However, this difference dropped to 34 % when considering only SM. Generally, suckling resulted in a 424 kg and 323 kg increase in milk yield for LY and HY Boran cows, respectively (Table 2).

S and HY cows produced 373 kg and 400 kg more (P<0.01) total milk than NS and LY cows, respectively. The longer lactation length (21 days more) for LY than LY cows partly attributed for the increased yield for this latter group. S*HY cows produced significantly (P<0.01) the highest total milk, while the lowest yield was recorded for NS*LY cows (Table 2). The report by Flavey and Chantalakahana (1999) indicated that apart from the suckling stimulation, the presence of the calf near its dam, and the degree of direct contact, smell and sound, can improve milk let down. The results of the current study support this finding. This as indicated by Foley et al (1973) is associated with the increased initiation of oxytocin release of the dam in the presence of the calf.

S cows consumed 1 kg and 1.4 kg more (P<0.01) concentrate and total DM daily respectively than NS cows. HY cows, on the other hand consumed 0.6 kg and 0.8 kg more concentrate and total DM daily respectively than LY cows. Daily concentrate, hay and total feed DM intakes were 1.6 kg, 0.7 kg and 2.3 kg, respectively higher (P<0.05) for S*HY cows than NS*LY cows (Table 3).

Some researchers indicated that high producing cows showed high protein requirement (Gardner and Park 1973), particularly in early lactation (Sparrow et al 1976). This might explain the findings of the present work where higher milk production of the suckling than non-suckling cows corresponded with more concentrate and total DMI. Chamberlain (1993) also indicated the direct association between feed intake and milk yield.

As treatments were imposed after calving, no apparent difference was observed on calf birth weight (Table 4). Generally suckling resulted in improved (P<0.01) average daily weight gain up to 3 and 5 months of age as compared to bucket-fed calves. This could best be explained by the higher amount of milk and milk fat consumed by suckling calves and the associated improved health conditions of the calves. Male calves generally grew faster than female calves up to both ages considered. Within the suckling group, male calves of high-yielding cows gained on average 0.2 kg and 0.19 kg more weight daily at 3 and 5 months respectively than female calves of low-yielding cows (Table 4).

The overall mean days of calving to first heat, calving to first service (days open) and number of cows not cycled were 119, 132 and 0.5, respectively (Table 5). SHY cows markedly (P<0.05) stayed longer without showing heat, followed by SLY cows. NS cows generally came in heat apparently (P<0.05) earlier than the suckling ones. Days open for S and NS cows was significantly (P<0.05) different with similar trend as that of calving to first heat. Two cows out of 18 from S group did not cycle during the experimental period.

The reproduction results obtained in this study are in line with previous reports (Gebre-Yohannes et al 1999; Tegegne 1989 and Tegegne et al 1994). Flavey and Chantalakahana (1999) indicated that a number of endogenous and exogenous factors have been reported to contribute to the delay or advancement of reproductive efficiency in cows. Suckling regimes (frequency and duration) and weaning age of calves were for instance reported to influence the cycling of cows. According to Tegegne (1989) restricted suckling (twice a day) at Gobe ranch (central Ethiopia) in Arsi (Ethiopian zebu breed) cattle reduced post partum anoustrous interval and increased pregnancy rate.

As one would expect the monthly milk yield considered in relation to milk chemical composition was only that obtained through hand milking. This is because deteriming the chemical composition of suckled milk is not practical and this explains the markedly higher milk yield of non-suckling cows than suckling cows.

Percent of fat in milk was 0.3% higher for NS than S, 0.6% higher for LY than HY and 0.6 % higher for dry season calved cows than those calved during the wet season. Percent protein in milk was 0.2 % higher for wet season calved than dry season calved cows, while % total solids were 0.3 higher for NS than S and 0.9 % higher for LY than HY cows (Table 6).

The significantly higher percent milk fat of NS cows might be due to the suckling effect whereby calves suckled their cows before and after hand milking. This result agrees with O'Connor (1994) who indicated that the first milk drawn from the udder contains about 1.4 % fat while last milk or stripping contains about 8.7 % fat. However, due to incomplete milking if fat is left in the udder at the end of a milking; it is usually picked up during subsequent milkings. Much of the fat therefore might have been picked up by the calves in S group that suckled before and after milking as indicated earlier resulting in low fat content of the HMM samples than that of the NS group. This also justifies the higher weight and growth rate recorded for calves of suckling cows at the ages considered. The inverse relationships between milk yield and % fat in the milk as indicated by Chamberlain (1993) could explain the apparently higher milk fat percent observed in LY cows.

The higher % fat of milk in NS than S and LY than HY corresponded to the higher total solids. The speculation for the marked difference in monthly milk yield, % fat and % protein in milk between calving seasons could be the environmental variation incurred due to seasonal changes that have important effects on the nutritional values of the feeds used (Sileshi et al 1996).

Conclusions

• Milk production potential of indigenous cows is higher in traditional milking practices (partial suckling) as stimulation by their calves proved to boost milk yield. Suckling improved milk production of indigenous cows and growth rate of their calves. It could thus be applied in the production of F₁ crossbred calves under smallholder production system, which can also accelerate heifer rearing and improve overall herd productivity.

• The effect of suckling on daily dry matter intake, milk yield and milk compositions was important. Although partial suckling resulted in reduced % fat in milk obtained through hand milking, total milk yield increased. Despite its advantage in terms of milk yield and calf growth, suckling prolonged calving to first heat, days open and increased number of services per conception. It's effect on lifetime productivity remains to be the focus of future concern. Similar studies need to be undertaken under different production systems to determine the most appropriate strategy for improving reproduction traits, milk production, calf growth and survival with suckling practices.

• The choice for partial suckling for increased productivity of local cows in the tropics in general and in Ethiopia in particular should consider improved feeding as the principal management tool. Further study is needed in this line to address the economic implications of such practice.

Acknowledgment

The financial support of the Ethiopian Agricultural Research Organization (AERO) is highly appreciated. The authors are grateful to technical staffs for the technical assistance rendered.

References

Beal W E, Notter D R, and Akers R M 1990 Techniques for estimation of milk yield in beef cows and relationship of milk yield to calf weight gain and postpartum reproduction. Journal of Animal Science. 68:937-947. http://jas.fass.org/cgi/reprint/68/4/937

Bruckmaier RM 2001 Milk ejection during machine milking in dairy cows. Livestock Production Science. 70: 121-124.

BSI 1989 Determination of fat content of milk and milk products (Gerber method), British Standards Institute (BSI). British Standard BS 696. Part II.

Chamberlain A 1993 Milk production in the tropics. Intermediate Tropical Agricultural Series, Longman Scientific and Technical, England, UK.

Delta Instruments 2000 Lactoscope. Postbus 379, 9200 AJ drachten, De Bolder 68, Holland.

EIAR 1976 Results of cattle crossbreeding program in the Ethiopian Institute of Agricultural Research (IAR), Addis Ababa, Ethiopia.

Flavey L and Chantalakahana C (editors) 1999 Smallholder dairy in the tropics. ILRI (International Livestock Research Institute) Nairobi, Kenya. 462 pp.

Foley C R, Donald L B, Frank N D and Allen T H 1973 Dairy cattle: Principles, practices, problems, and profits. Lea and Febiger. Philadelphia.

Gardner R W and Park R L 1973 Protein requirements of cows fed high concentrate rations. Journal of Dairy Science. 56: 390.

Gebre-Yohannes G E, Kumsa T, Tola A and Asfaw C 1999 Effect of Suckling on calf preweaning growth and cow reproduction in Horro and crossbred cows. In: Proceedings of the 7^th Annual Conference of the Ethiopian Socity of Animal production (ESAP) held in Addis Ababa, Ethiopia, 26-27 May 1999, pp 212-216.

Gojjam Y, Yilma Z, Bekele G, Gebre-Wold A and Demeke S 2002 Milk yield and reproductive performance of Boran cows and growth rate of their calves under partial suckling method. In: Proceedings of the 9^th Conference of the Ethiopian Society of Animal Production (ESAP), Ethiopian Agricultural Research Organization (EARO), Addis Ababa, Ethiopia.

Kebede B 1984 Improving Ethiopia's milk production. The potential for small-scale milk production in Eastern and Southern Africa. International Development Research Center, Canada. pp. 19-26.

Kumssa T and Gebre-Yohannes G E 1995 Effect of suckling on dairy performance of local and crossbred cows. I. Milk yield and lactation length. In: Proceedings of the 3^rd Conference of The Ethiopian Society of Animal Production (ESAP), 27-29 April 1995 Addis Ababa, Ethiopia, PP 135-139.

Little D A, Anderson F M and Durkin J W 1989 Partial suckling of crossbred dairy cows: Initial results on effects of milk off-take and calf growth at Debre Birhan. In: Proceedings of the 2^nd National Livestock Improvement Conference. 24-26 Feb. 1988. Addis Ababa. Ethiopia. pp. 92-98

Marth H 1978 Standard methods for the examination of dairy products (14^th edition). American Public Health Association, Washington, D.C.

McDonald P, Edwards R A, Greenhalgh J F D and Morgan C A 1995 Animal Nutrition. 5^th edition. Longman Scientific and Technical. Co-published in the United States with John wiley and Sons, Inc., New York. 607 pp.

Mukasa-Mugerwa E 1989: A review of reproductive performance of female Bos indicus (zebu) cattle. ILCA Monograph. No. 6. International Livestock Centre for Africa. Addis Ababa, Ethiopia.

O'Connor C B 1994 Rural dairy technology. ILRI training manual No.1. International livestock Center for Africa, Addis Ababa, Ethiopia. 133 pp.

Pyne G T 1932 The determination of milk proteins by formaldehyde titration. Biochemistry Journal 26: 1006-1014.

SAS 2001 User's guide: Statistics, version 5, SAS Institute. Statistical Analysis System (SAS). Inc. Cary, NC.

Sileshi Z, Bediye S, Gebre Hiwot L and Tekle Tsadiq T 1996 The effect of harvesting stage on the yield and quality of natural pasture in the central highlands of Ethiopia. 3^rd Conference of the Ethiopian Society of Animal Production (ESAP) held on April 27 - 29 1995, Addis Ababa, pp 27 - 29.

Sparrow R C, Hemken R W, Jacobson D R, Button F S and Enlow C M 1976 Effect of three protein percent on nitrogen balance, body weight change, milk production and composition of lactating cows during early lactation. Journal of Dairy Science 56: 664 (Abstract).

Tedla A, Tefera G M, Gebre-Wold A, Yemane B and Philip C 1991 Status of Dairying in Ethiopia and Strategies for Future Development. In Proceedings of the Third Livestock Improvement Conference, 24-26 May 1989, Institute of Agricultural Research, Addis Ababa, Ethiopia. pp. 25-36.

Tegegne A 1989 Reproductive development and function in zebu and crossbred cattle in Ethiopia. PhD Thesis. James Cook University, Australia.

Tegegne A, Geleto F, Osuji P O, Kassa T and Franceschini R 1994 Influence of dietary supplementation and partial suckling on body weight and on lactation and reproductive performance of primiparous Borana (Bos indicus) cows in Ethiopia. Journal of Agricultural Science. Cambridge. 123. 267-273.

Yilma Z 1999 Smallholder milk production systems and processing techniques in the central highlands of Ethiopia. MSc Thesis, Swedish University of Agricultural Sciences. Uppsala. Sweden.