Milk yield and reproductive performances of lactating cows as affected by intakes of certain dietary macro minerals in Ethiopia

N Tolla and P Vijchulata^*

Adami Tulu Agricultural Research Center, P.O. Box 35 Ziway, Ethiopia
raggatu@yahoo.com
*Department of Animal Science, Faculty of Agriculture, Kasetsart University, Bangkok 10900 Thailand

Abstract

This study was conducted to investigate the influences of dietary intakes of certain minerals on milk yield and reproductive performances of lactating cows fed on concentrate supplement with/without cottonseed cake and/or bole soil. Thirty-two pregnant Holstein Friesian cows with average body weight of 524±54 kg were blocked by their expected due date of calving as early (B1) and late (B2). Soon after calving animals were assigned in a randomized complete block design to one of the following four dietary treatments: concentrate alone (control) (C), 45% of the concentrate diet by weight substituted with cottonseed cake (C + CSC), concentrate plus 3% bole (lake soil) (C + Bole) and 45% of the concentrate substituted with cottonseed cake plus 3% bole (C + CSC + Bole) for 135 days of data collection.

Statistically daily milk yield and FC milk yield were not ifferent among treatments. However, animals fed on the treatment diets of concentrate + CSC, concentrate + Bole and concentrate + CSC + Bole, produced 7.4, 16.3 and 18.2% respectively higher actual milk and 14.3, 24.2 and 25.7% respectively higher 4% fat corrected milk than the control group. Inclusion of bole soil alone as a mineral source or in combination with CSC supported higher daily actual and FC milk production than feeding concentrate diet with CSC alone. Days from calving to first estrus, days open and number of services per conception were not different among treatments. Nevertheless, Shorter intervals of days from calving to first estrus, days open and lowest number of services per conception were recorded for animals fed on concentrate diet with bole soil alone followed by those fed the control diet. Inclusion of 3% bole soil alone appeared to improve both milk yield and reproductive performances of dairy cattle.

Key words: bole soil, cottonseed cake, cows, Ethiopia, milk yield, minerals, reproduction

Introduction

Proper mineral nutrition and supplementation is essential to animal health and high level of milk production (Harris et al1994). Most of the diets of ruminant are plant materials and the amount of minerals present in the plants depends upon the mineral status of the soil on which the herbage grows, the ability of the plant to absorb them and the stage of growth of the plant. The levels of minerals can even vary from field to field on the same farm (Chesworth and Guérin 1992; Preston and Leng 1987). Therefore, it is very difficult to give average values for the amount of minerals, which might be expected from feeds. Grains are low in calcium content but higher in phosphorus. Legumes usually are good sources of calcium but not phosphorus, and grasses are much lower in calcium than legumes (Schroeder 2004).

Most dairy farmers in Ethiopia heavily rely on mill by products rather than mixed concentrates. The mix of available concentrate feeds also largely depends on available materials and quantity than the requirement and quality of nutrients. The most commonly used feed resources for dairy animals are natural grass hay, wheat bran and middling and noug seed (Guizota abyssinica) cake (Staal and Shapiro 1996). Cottonseed cake is also one of the available oil seed cakes widely used as protein source in fattening operations. Cottonseed cake is considered as a rumen bypass protein source (Preston and Leng 1987) and good source of phosphorus. However, it is rarely utilized in commercial dairy farming system in Ethiopia and information on its influence on productive and reproductive performances of dairy cattle is limited. Levels of essential minerals in most commonly used fibrous feed resources in Ethiopia were studied and reported to be deficient to marginal (Kabaija and Little 1989). Evaluation of mineral compositions of locally produced oilseed cakes has also indicated that the concentration of P, K and Mg are higher than optimum level for ruminant diets but low in Ca and Na contents (Solomon 1992). But their availability for utilization is influenced by the level of fiber in the feed, because of its association with some indigestible fibers (Kabaija and Little 1989). The existing animal feed processing firms include limestone and common salt (NaCl) in concentrate mixtures as mineral source depending on availability. A salty, lake soil locally known as bole is also abundantly and cheaply available in the central rift valley lake of Abiyata and used by local farmers as mineral source for their animals. However, documented information on the nutritive value and influences of bole soil on milk production and reproductive efficiency of dairy cows is scarce. Therefore, this study evaluated milk yield and reproductive performances of lactating dairy cows fed native grass hay and a concentrate supplement with/without cottonseed cake and/or bole soil.

Materials and methods

Study area

This study was conducted at Holeta Dairy Farm belonging to cattle genetic improvement center of Federal Ministry of Agriculture, Ethiopia. The farm is located at about 44 km to the West of Addis Ababa, at 9^o3'N latitude and 38^o30'E longitude. It has an altitude of 2390 meters above sea level and receives an average annual rainfall of about 1700-mm. The rainfall is erratic and bimodal with the main rains occurring from June to September. The minimum and maximum average temperature is 6.3^oC and 22.1^oC respectively.

Animals and management

Thirty-two pregnant Holstein Friesian cows with average body weight of 524±54 kg were blocked by their expected due date of calving as early (B1) and late (B2). Soon after calving animals were assigned in a randomized complete block design to one of the four dietary treatments of concentrate alone (control) (C), 45% of the concentrate diet by weight substituted with cottonseed cake (C + CSC), concentrate plus 3% bole (lake soil) (C + Bole) and 45% of the concentrate substituted with cottonseed cake plus 3% bole (C + CSC + Bole). Data on milk yield and feed intake were collected on daily basis starting from day one postpartum for 135 days. The composition of the commercially formulated concentrate (control) diet was wheat bran (55%), wheat middling (10%), noug seed (Guizota abyssinica) cake (30%), limestone (3%) and common salt (2%). The CSC used in this trial was from mechanical oil extracting factory. Animals were individually penned and fed with ad libitum native grass hay predominantly composed of Digitaria, Eragrostis and Trifolium species. The experimental diets were offered at the rate of 0.5kg per kg of milk yield in two equal feedings before the morning and evening milking. Water was offered three times daily in the morning, noon and evening. Animals were hand milked twice daily at 6 to 7 AM and 4 to 5 PM and daily milk yield was recorded accordingly. Data for feed intake and refusals were recorded on daily basis. Feed samples were collected weekly, bulked, sub-sampled and delivered to laboratory for chemical analysis. Any sign of estrus manifestation was visually observed and recorded by artificial inseminator (AI) technician three times daily, early morning, noon and late after-noon. Animals in heat were inseminated with AI after 7 to 8 hours of observed estrus.

Chemical analysis

Feeds were analyzed for Calcium (Ca), sodium (Na), potassium (K), magnesium (Mg) and manganese (Mn) contents using atomic absorption spectrophotometers according to Perkins (1982), and phosphorus (P) content was determined using auto analyzer according to AOAC (1995). The intakes of minerals were estimated by multiplying dry matter intake (DMI) of the feeds with the values of their respective mineral concentration according to Kearl (1982) and MAFF (1985).

Statistical analysis

Data were analyzed using the general linear model (GLM) procedure of SAS (1999). Differences between treatment groups on intake of feeds and nutrients, milk yield and reproductive efficiencies were evaluated using Duncan multiple range test. The model used to analyze the treatment effects on milk yield and milk composition was:

Y = µ + b_i + t_j + e_ij

Where,

Y = means for response variables
µ = overall mean
b = effects of i^th block (b = 1, 2)
t = effects of j^th treatment (t = 1, 2, …4)
e = error term

Results and Discussion

Mineral composition of experimental feeds

Mean macro-mineral composition of the experimental diets is presented in Table 1.

Grass hay was below critical levels suggested by McDowell (1997) in P, Na and Mg contents. But Ca content of the grass was slightly above the critical level and also higher than the values reported by Vijchulata (1998) for different species of grasses in Thailand. This may be due to the fact that the composition of the grass hay consisted of Digitaria, Eragrostis and Trifolium species unlike the pure stand grass varieties studied by Vijchulata (1998). The slightly higher Ca content of the mixed grass in this study may be attributed to its Trifolium content. In addition, the concentration of mineral elements in forage depends upon the interaction of several factors such as soil, plant species, stage of maturity and climate (McDowell 1997; Chesworth and Guérin 1992). The ratio of Ca to P in grass hay was also sufficiently above the critical level. All the dietary concentrate mixtures were sufficient in all the minerals under consideration. The ratio of Ca to P in the dietary treatments of concentrate alone and concentrate + Bole were also sufficient, but in the treatments of concentrate + CSC and concentrate + CSC + bole soil it was below critical levels suggested by McDowell (1997). Calcium, Na and Mn contents of cottonseed cake was below the critical levels, while P, K and Mg contents were sufficiently above the critical levels for ruminant diets and this agrees with the report of Solomon (1992). Bole soil was below critical in Ca, P, Mg and Mn contents and sufficiently high in Na K contents.

Dietary minerals intake

The estimated dietary intakes of minerals by lactating cows fed grass hay and concentrate supplement with/without cottonseed cake and/or bole soil are presented in Table 2.

There was sufficiently higher intake of Ca by animals fed on the dietary treatment concentrate + bole followed by those fed on concentrate diet alone (control). The intake of P was sufficient throughout all the treatment groups. The intake of Na was deficient for animals fed on the dietary treatment of concentrate + CSC, slightly above the marginal level for the control group and sufficiently higher than requirement for animals fed on dietary treatment of concentrate + bole followed by those fed on concentrate + CSC + bole. There was sufficiently higher intake of K throughout all treatment groups while intake of Mg was not much far from marginal level in all treatments. Intake of Mn was higher than requirement in all treatments. The higher levels of Mn in all treatments were attributed to higher concentration of the element in grass hay. The reason for relatively lower concentrations of Ca, Na and Mn in the dietary treatment of concentrate + CSC than the other treatment groups may be due to lower concentrations of these elements in CSC (Table 1).

Milk yield and reproductive efficiency

Milk production and reproductive performances of lactating cows fed on grass hay and concentrate supplement with/without cottonseed cake and/or bole soil is presented in Table 3.

Daily milk yield and FC milk yield were not significantly (p>0.05) different among treatments. However, animals fed on the treatment diets of concentrate + CSC, concentrate + Bole and concentrate + CSC + Bole, produced 7.4, 16.3 and 18.2% respectively higher actual milk and 14.3, 24.2 and 25.7% respectively higher 4% fat corrected milk than the control group. Inclusion of bole soil alone as a mineral source or in combination with CSC supported higher daily actual and FC milk production than feeding concentrate diet with CSC alone. This may be attributed to relatively higher dietary concentration of Na in these two treatment groups (Table 3). Sanchez et al (1994a, b) and Berger (1994) reported that dry matter intake and milk yield was improved by dietary concentration of Na above those needed to meet requirements. Dry matter intake and milk yield responses over a range of dietary Na concentrations (0.11 to 1.2 %DM) were curvilinear, with maximum performance at 0.70 to 0.80 percent of dry matter (Sanchez et al 1994a, b). In addition the higher milk yield responses of animals fed these diets may be also the result of higher concentrations of  K.  Sanchez et al (1994a, b) further reported that there was higher DM intake and milk yield responses at higher concentration of K above those needed to meet requirements. Dry matter intake and milk yield responses over a range of dietary potassium concentrations (0.66 to 1.96 %DM) were curvilinear, with the maximum performance when diets contained 1.50 percent potassium, dry matter basis. Maximum feed intake and milk yield responses at higher concentrations of potassium than needed to meet requirements likely are associated with the higher concentrations of sodium. Interactions of potassium by sodium on DM intake and milk yield indicated that responses to potassium differed over the range of dietary concentrations of sodium.

Days from calving to first estrus, days open and number of services per conception were not different (p>0.05) among treatments (Table 3) Nevertheless, longer intervals of days from calving to first observed estrus, days open and higher number of services per conceptions were observed for animals fed on concentrate diet with CSC alone, which may be due to marginal concentration of Na in this dietary treatment. Shorter intervals of days from calving to first estrus, days open and lowest number of services per conception were recorded for animals fed on concentrate diet with bole soil alone followed by those fed the control diet. This may be attributed to sufficiently higher dietary intake of Ca, P, Na and Mn as well as the relatively higher ratio of Ca to P in these dietary treatments (Table 3). Balanced mineral supply is strongly associated with reproductive performances of dairy cows (Lanyasunya et al 2005). Feeding Ca deficient diet may delay uterine involution, and fertility can also be impaired by feeding diet with Ca: P ratio of less than 1.5 or greater than 3.5 (Shaver and Howard 2005). Although, dietary P concentration was more adequate than needed to meet the requirement throughout the treatments it could not equally improve reproductive efficiencies of animals in treatments, Concentrate + CSC and concentrate + CSC + bole, as those fed the concentrate (control) or concentrate + bole soil treatments, may be due to marginal levels in the concentration of Ca in these treatment and the interaction of the two mineral elements. Shaver and Howard (2005) reported that high P intakes along with low Ca intakes depressed fertility in dairy cows. The relatively higher dietary concentration of K than needed to meet requirements in treatments with CSC alone or its combination with bole may be also one of the possible reasons for lower reproductive performances of animals under these treatments. Lanyasunya et al (2005) reported that feeding high level of K delayed ovulation in dairy cattle. Even though the concentration of Mn was sufficiently higher than the requirement throughout the treatment groups the levels in the dietary treatments with CSC was depressed and can be related to lower reproductive efficiencies of animals under these treatments. Manganese is one of the trace minerals associated with ovarian function. Cows fed on low manganese diets were slower to exhibit estrus, more likely to have silent heat and lower conception rate than cows fed sufficient manganese in their diets (Rojas et al 1965). The trend in reproductive responses of animals to the levels of Ca, Na, P, and Mn indicates the interactions of these mineral elements.

Conclusions

• Substitution of a concentrate diet with 45% CSC in the dietary treatment of concentrate + CSC and concentrate + CSC + Bole depressed dietary concentrations of Ca, Na, Mg and Mn and appeared to increase the interval days from calving to first estrus, days open and number of services required per conception than feeding concentrate (control) or concentrate with bole alone.

• Inclusion of CSC in a concentrate diet either alone or in combination with bole appeared to have a negative influence on reproductive efficiency of lactating cows, increasing interval days from calving to conception and the number of services needed per conception in this trial. I

• nclusion of 3% bole soil alone appeared to increase both milk yield reproductive performances of dairy cattle.

Acknowledgements

The authors express their appreciation to the managements of Kaliti Artificial Insemination Center and Cattle Genetic Improvement Center at Holeta for kindly giving us access to the experimental animals and farm facilities. The Oromia Agricultural Research Institute (OARI) is gratefully acknowledged for funding this study. The unreserved assistance of Mr. Amare Atale in undertaking the statistical analysis is highly appreciated.

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Received 9 May 2006; Accepted 16 June 2006; Published 11 September 2006

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