| Livestock Research for Rural Development 19 (12) 2007 | Guide for preparation of papers | LRRD News | Citation of this paper |
A study was carried out to analyze and compare percentages of milk fat, protein, lactose and total solids content of Borana and Boran-Friesian crossbred dairy cows across seasons to evaluate the grazing management of dairy cows. The study was aimed to plan proper feeding strategies across seasons in line with feed supply situations of the grazing pastureland based on recommendations drawn from results of this study.
Regardless of the effect of seasons, Boron cows showed higher percentage of milk fat, protein and total solids content than Friesian crossbred cows. However Friesian crossbred dairy cows showed higher content of milk lactose than local Borana cows. Highest milk fat content of Friesian crossbred dairy cows was observed in July to September and the lowest was in April to June. Highest milk fat, protein and total solids contents of local Borana cows were observed in October to December and the lowest in January to March. Friesian crossbred dairy cows had highest milk protein in July to September and the lowest in January to March. However milk lactose content of Borana and Boran-Friesian crossbred dairy cows did not differ across seasons. Milk total solids content of Boran-Friesian crossbred dairy cows was highest in July to September and the lowest in January to March. Milk fat and protein contents of Boran and Boran-Friesian crossbred dairy cows were higher in July to September and October to December as compared to rest of the seasons. Similarly total solids content of Boran cows was higher in July to September and October to December as compared to rest of the seasons.
Feeding management should be planned and implemented to Borana and Boran-Friesian crossbred dairy cows across seasons independently. There is a need to properly feed dairy cows particularly in seasons when shortage of grazing land affects milk composition.
Key words: Fat, lactose, season, total solids
Cow breeds indigenous to Ethiopia are characterized by: high values for milk composition, low milk yield (hardly exceeds 600 liters in a short lactation of less than 200 days), a long time to get the first calf (ranging from 3.5 to 4 years) with long calving interval (Kiwuwa et al 1983; Beyene 1992; Sendros et al 2003).
To improve milk productivity of local cows, crossbreeding with exotic breed was proved to be promising for the highlands and mid altitude zones of Ethiopia (McDowell 1985a; McDowell 1985b; Mohammed et al 1987; Sendros et al 1987a; Sendros et al 1987b; Beyene 1992; and Sendros et al 2003). To undertake continued crossbreeding activities, the Holetta Agricultural Research uses local Borana cows and exotic Friesian semen to produce Boran-Friesian crossbred dairy cattle, which have been reported to be promising for the highlands of Ethiopia (Beyene 1992; Mengistu et al 2000; Solomon 1996; Zerbini et al 1993).
The nutritional value of milk is high. It contains fat, protein, lactose, minerals, vitamins and enzymes mixed in water. Milk constituents therefore are very important to dairy product manufacturers. They influence the yield of butter and cheese. Besides milk yield, composition of milk has become more important due to the rise in price of butter and cheese in recent years in Ethiopia. Thus, milk composition is becoming a crucial factor in determining profitability of dairy farming.
The composition of milk varies considerably with breed type, stage of lactation, feed, season of the year, and many other factors (Charles 1998). The cow’s diet is the ultimate source of most of the material used in milk synthesis. The conditions of feeding and the rations fed to the cow influences the percent and yield of milk composition (Robinson 1997). The nutritional status of cows in relation to optimization of milk constituents can be adjusted through proper grazing and feeding management (Robinson 1997). This study therefore is aimed at investigating the grazing status of Borana and Boran-Friesian crossbred dairy cattle breeds through analysis of milk composition across seasons. Evaluation of the grazing situation is a goal to plan improved feeding strategy in line with the grazing regimes of the pastureland so as to maximize productivity of dairy cattle. This will help to foster proper feeding recommendations when crossbred dairy cattle are released to smallholder farmers.
The study was carried out at Holetta Agricultural Research Center (HARC). Holetta is one of typical highland areas of Ethiopia, which is literally conducive for smallholder dairying. It is located at 45km west of the capital City, Addis Ababa with an altitude of 2400 meters above sea level. It is situated at 90 3’N latitude and 380 38’ E longitudes. The area receives an annual rainfall of 1100 mm with an average maximum temperature of 21.3oC (18.6-24oC).
Two breeds of cows were used for the study. Borana cows are local to Ethiopia. They are used as dam breeds for the crossbreeding activities. They are bred with exotic Friesian sire (semen) to produce Boran-Friesian crossbred cattle. The second breed type is crossbred of Boran-Friesian dairy cows, the one recommended promising to release to the smallholder farmers.
The feeding system of dairy cows at Holetta Agricultural research centre is roughage based and supplemented with concentrate feeds (mixture of 31% wheat bran, 33% wheat middlings, 35% noug cake and 1% common salt. The supplementation status of concentrate feeds is similar across the entire year. However, the supply of roughage from the grazing pastureland varies with seasons.
Among the four seasons, dairy cows were allowed to graze on natural pasture of the dairy farm for three consecutive seasons (October to December, January to March, and April to June). They graze for approximately 8:00 hrs in a day from 7:00 hours to 15 hours. However, during the heavy rainy season (July to September), the grazing pastureland is protected from grazing for purpose of producing hay to be used as roughage feed for the entire year. During this season, dairy cows are restricted to little grazing on back yard of the research campus. They are supplemented with ample cut and carry of green grass and little conserved hay. For the whole year, milking cows are supplemented with mixture of local concentrate feeds during milking.
The pasture hay is harvested starting from October to November. After harvesting cows are released to graze and they consume ample left over from the harvested pastureland. Through time, particularly during April to June, the left over gets diminished.
Data of 3 years (2003-2005) were collected and analyzed for fat, protein, lactose and total solids contents of milk from Boran and Boran-Friesian crossbred dairy cows. Milk Samples from morning and evening milkings were collected and make a composite. Laboratory analysis for milk fat, protein lactose and total solids was investigated based on the scientific procedures of the Lacto scope machine.
Data close to 13162 were used for analysis. Fat, protein, lactose and total solids contents of milk were subjected to Analysis of Variance using General Linear Model (GLM) procedures of SAS (Statistical Analysis System Institute release 6.12, 1999).
Since the study was based on laboratory analysis, a higher precision is expected in procedures of measurements and laboratory analysis. Thus the probability level used to compare variations between milk compositions of breeds of cows across seasons was at 1%.
The statistical model used was:
Yijk=µ + ti + e i
Where:
Yijk is the dependent variable (milk fat, protein, lactose and total solids)
µ is overall mean
ri is effect of treatment
ei random variation.
The investigation made to compare milk compositions between the two breeds showed that, there are significant (P<0.01) differences on all milk compositions between Borana and Friesian crossbred dairy cows (Table 1). i.e., Boran cows have shown significantly (P<0.01) higher percentage of milk fat, protein and total solids than Friesian crossbred cows. Whereas Friesian crossbred dairy cows have shown significantly (P<0.01) higher content of milk lactose than Borana cows.
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Table1. Milk fat, protein, lactose and total solids percent of Boran and Boran-Friesian crossbred dairy cows |
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Milk composition, % |
LS-Means and SE, % |
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Boran-Friesian cross |
Borana cows |
|
|
Milk fat |
5.48 ± 0.02a |
6.01 ± 0.05b |
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Milk protein |
3.80 ± 0.03a |
4.05 ± 0.05b |
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Milk lactose |
4.18 ± 0.05a |
4.00 ± 0.05b |
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Milk total solids |
15.32 ± 0.03a |
16.02 ± 0.05b |
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ab Least square means with different superscripts within row differ at P<0.01 |
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The analysis made to examine situation of milk composition of Boran-Friesian crossbred dairy cows across different seasons showed that, significantly (P<0.01) highest milk fat content was observed during July to September and the lowest was recorded during April to June Table 2).
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Table 2. Milk fat percent of Boran-Friesian crossbred dairy cows across seasons |
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Season |
Ls-Means and SE, % |
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January to March |
5.47 ± 0.05a |
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April to June |
5.39 ± 0.04a |
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July to September |
5.60 ± 0.05 b |
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October to December |
5.46 ± 0.05a |
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abLeast square means with different superscripts within column differ at P<0.01 |
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Concerning milk compositions of Borana cows across different seasons, significantly (P<0.01) highest milk fat content was observed in October to December and the lowest was recorded in January to March (Table 3).
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Table 3. Milk fat percent of Boran cows across seasons |
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Season |
Ls-Means and SE, % |
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January to March |
5.65 ± 0.13 a |
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April to June |
5.69 ± 0.13 a |
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July to September |
6.29 ± 0.13 b |
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October to December |
6.51 ± 0.13bc |
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abc Least square means with different superscripts within column differ at P<0.01 |
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Regarding to percentage of milk protein across different seasons, Friesian crossbred dairy cows have shown the highest protein content in July to September and the lowest was in January to March. Milk protein content of Friesian crossbred dairy cows in April to June, July to September and October to December were significantly (P<0.01) higher than January to March (Table 4).
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Table 4. Milk protein percent of Boran-Friesian crossbred dairy cows across seasons |
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Season |
Ls-Means and SE, % |
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January to March |
3.63 ± 0.052 a |
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April to June |
3.84 ± 0.048b |
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July to September |
3.86 ± 0.048b |
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October to December |
3.85 ± 0.048cb |
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abcLeast square means with different superscripts within column are differ P<0.01 |
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In the case of Borana cows (Table 5), they have recorded significantly (P<0.01) highest milk protein content in October to December and the lowest was in January to March.
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Table 5. Milk protein percent of Borana cows across seasons |
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Season |
Ls-Means and SE, % |
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January to March |
3.88 ± 0.04 a |
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April to June |
3.96 ± 0.04 a |
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July to September |
4.14 ± 0.04 b |
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October to December |
4.25 ± 0.04 bc |
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abcLeast square means with different superscripts within column differ at P<0.01 |
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As indicated in Table 6, the analysis made to compare milk lactose content of Borana-Friesian crossbred dairy cows across seasons showed that, lactose percent of milk in April to June appeared significantly (P<0.01) higher than the rest of the seasons.
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Table 6. Milk lactose percent of Boran-Friesian crossbred dairy cows across seasons |
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Season |
Ls-Means and SE, % |
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January to March |
4.16 ± 0.015 a |
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April to June |
4.22 ± 0.014 b |
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July to September |
4.16 ± 0.014 cd |
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October to December |
4.16 ± 0.014 ac |
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abcdLeast square means with different superscripts within column differ at P<0.01 |
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As indicated in Table 7, milk lactose content of Borana cows in January to March was the highest and the lowest was in October to December. Significantly (P<0.01) highest milk lactose appeared in January to March.
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Table 7. Milk lactose percent of Boran cows across seasons |
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Season |
Ls-Means and SE, % |
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January to March |
4.07 ± 0.04 a |
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April to June |
4.01 ± 0.04 ab |
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July to September |
4.03 ± 0.04 a |
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October to December |
3.86 ± 0.04 b |
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abLeast square means with different superscripts within column are differ at P<0.01 |
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As shown in Table 8, milk total solids content of Boran-Friesian crossbred dairy cows was significantly (P<0.01) highest in July to September and October to December and the lowest was in January to March.
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Table 8. Milk total solids percent of Boran-Friesian crossbred dairy cows across seasons |
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Season |
Ls-Means and SE, % |
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January to March |
15.10 ± 0.08 a |
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April to June |
15.28 ± 0.07 ac |
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July to September |
15.52 ± 0.07cd |
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October to December |
15.35 ± 0.07abd |
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abcdLeast square means with different superscripts within columns differ at P<0.01 |
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As indicated in Table 9, milk total solids of Borana cows were significantly (P<0.01) highest in October to December and the lowest was in January to March.
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Table 9. Milk total solids percent of Boran cows across seasons |
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Season |
Ls-Means and SE, % |
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January to March |
15.47 ± 0.19 a |
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April to June |
15.59 ± 0.19 a |
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July to September |
16.48 ± 0.19 b |
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October to December |
16.66 ± 0.19 b c |
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abcLeast square means with different superscripts within column differ at P<0.01 |
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The result of this study showed that the different breeds (Boran and crossbred Boran-Friesian) have showed significant variation in milk constituents (Table 1). Boran cows have showed higher percentage of milk fat, protein and total solids content than Friesian crossbred cows. These findings have similarity with results of Gonthier et al (2005) that reported the type of breed affects milk composition. Total solids of milk produced by Holstein cows averaged 12.4% versus 14.6% for Jerseys. Holsteins produced less milk fat (3.7% vs. 5.1%), solids-not-fat (8.7% vs. 9.5%), and protein (3.1% vs. 3.7%). Holstein cows had 12.4%, 3.7%, 8.7%, 3.1%, 4.9% total solids, fat, solid-not-fat, protein and lactose respectively. Where as Jersey cows had 6%, 5.1%, 9.5%, 3.7% and 5% total solids, fat, solid-not-fat, protein and lactose respectively. Similarly Charles (1998) reported that Holsteins tend to have the lowest percentage milk composition as compared to Jersey, Ayrshire and Guernsey breeds.
The current study however showed that crossbred dairy cows have higher content of milk lactose than local Boran cows (Table 4). Corruthers (1993) reported that lactose production is genetically determined. There is a difference between Jersey and Holstein cows in lactose production. The differences in lactose production have an implication to milk production. Lactose production by the udder is responsible for milk water secretion through the osmotic effects exerted by lactose. Variation in lactose production between breeds of cows has two major consequences. First a high level of lactose production relative to fat and protein results in more dilute milk and also has increased the filling rate of the udder between milking. In this regard, udders of American Holstein cattle, which produce relatively dilute milk, are full within 18 h of milking, where as New Zealand Jersey cows producing a high solids content will take up to 29 h to fill the storage capacity of the udder. Such differences are significance in the quest for reducing milking frequency without production loss, which clearly can’t be achieved in Holstein type animals. Whereas milk lactose content of Boran and Borana-Friesian crossbred dairy cows didn’t significantly (P>0.01) differ across all the seasons. This finding has similarity with the results of Gonthier et al (2005) in evaluating percentage of milk constituents by feeding micronized and extruded flaxseed to dairy cows.
Milk fat, protein and total solids content of Boran-Friesian crossbred dairy cows were highest in July to September and next higher in October to December and the lowest was in April to June and January to March (Table 2, 4 and 8). The highest milk fat, protein and total solids content of Boran-Friesian crossbred dairy cows recorded in July to September is due to the fact that, dairy cows are restricted to limited grazing but are supplemented with adequate amount of green grass and legumes in a cut and carry system and little hay. Such feeds are able to provide adequate amount of energy and protein to the animal. Nutrients required for synthesis of adequate milk constituents are derived from the end products of rumen fermentation supplied by a balanced feeds, amongst which are the volatile fatty acids and microbial protein (Chenost and Sansoucy 1998). For that matter young grasses have a high feeding value and supply the cow with increased level of both ME and of CP. because leafy vegetative grasses are high quality feeds; as they mature their fiber and lignin contents increase steadily while percent protein and digestibility decrease (Harlan and Dale 1996).
The difference of milk composition between Borana and crossbred dairy cows across different grazing regimes may be due to the influences of breed differences in feed conversion efficiency to specific feed type. The result was consistent with findings of Rodriguez et al (1997) that the Jerseys showed greater efficiency of energy conversion than Holsteins.
The results of this study indicate that:
Regardless of the feeding management employed in different seasons, Borana cows have shown higher percentage of milk fat, protein and total solids content, and lower content of lactose than Friesian crossbred cows.
Percentages of milk fat, protein and total solids content of Boran-Friesian crossbred dairy cows were highest in July to September and lowest in January to March.
Milk fat, protein and total solids content of Borana cows were highest in October to December and lowest in January to March
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Received 4 April 2007; Accepted 11 November 2007; Published 11 December 2007