**Effects of Environmental Factors on Milk Yield, Lactation Length and Dry Period in Tunisian Holstein Cows**

Naceur M'hamdi, Mahdi Bouallegue, Saoussen Frouja, Yosra Ressaissi, Satinder Kaur Brar and Mohamed Ben Hamouda

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/50803

## **1. Introduction**

Management, nutrition, lactation turn or the age, year and season in which lactation started are the leading environmental factors affecting lactation performance in cattle. Beside these factors, the persistency level of the highest milk production period reached on lactation is a significant factor [1]. Also, lactation performance in dairy cattle depends upon genetic and environmental factors. Genetic background, climate, diseases, feeding, year and season of calving have been reported to affect milk production, lactation length and dry period [2, 3]. Breed, age, stage of lactation, parity and milking frequency also influence performance production [2, 3]. Holstein cows were considered the most dairy cows in the World. As number of Holstein cows in Tunisia is more than other breeds, breeding of Holstein cows is very important. Milk yield and duration of lactation have marked effects on dairy economy [4, 5]. The persistency level of lactation milk production can be defined as the ability of keeping a high daily milk flow during lactation, in the milk productivity of lactation's first period's persistency level or the rest of the lactation as a measure of lactation curve diagram, the highest period productivity of the continuation level during lactation, continuation level of the highest productivity and after reaching the highest productivity the rate of decreasing seen on milk production in time. Milk yield is the most important single determinant of profit for the dairy cow. Moreover, effects of lactation number, age, and season and year of calving on milk yield and lactation length are well known. In addition, in breeding of dairy cows, the most important aims are to obtain a calf in a year and high milk yield from cows. To obtain a calf in a year from cows depends on some parameters of ideal limits (60 days dry period, 305 days lactation duration etc.). However, profitable breeding could be achieved by keeping lactation

© 2012 M'hamdi et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 M'hamdi et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

duration, dry period and service period between optimal limits [6, 7]. The yields of farm animals are the result of the combined effects of genotype and environmental conditions. In order to increase the yield level, it is necessary to optimize the environmental conditions and to improve the genetic structure of the animals. In order to enhance productivity of a dairy animal, it is necessary to develop an understanding of the factors affecting its milk production. Environmental factors can be classified as factors with measurable effects (age, year, season, milking frequency, etc.) and factors with immeasurable effects (infectious diseases, parasitic infestations, etc.). The measurable effects can be determined and used in the management of the farm [8]. Environmental factors affecting variability in daily milk yield are widely documented in dairy cattle [9- 11]. The 305 days milk yield of Holstein cows was 5905 kg in Tunisia [12], 5353 kg in Morocco [13], and between 4597 and 6464 kg in Turkey [14- 16]. Environmental factors such as year of calving, season of calving and age at calving affect productivity [17]. Many researchers [6, 14] reported that the effect of calving season on 305 days milk yield was as significant and indicated that milk yield was higher in autumn and winter. Unlike, Bilgiç and Aliç [16] and Pelister et al. [18] reported that effect of calving season on 305 days milk yield was non-significant. Although, effect of lactation number on 305-days milk yield was reported [14, 15, 19] as significant. Opposing, Koçak et al. [6] and Bilgiç and Aliç [16] reported a non-significant effect of lactation number on 305 days milk yield. Effects of calving age on 305 days milk yield have been reported as significant [18, 20]. The lactation duration of Holstein cows was between 284.7 and 333.9 days in previous studies [14, 16, 21, 22]. The effect of calving season on lactation duration was reported as non-significant [6, 16, 18]. The effect of lactation number on lactation duration was reported as nonsignificant [14, 16, 19]. However, the effect of calving age on lactation duration was reported as significant [15, 18]. Zambrano et al. [23] reported that the effect of calving year on lactation duration was significant. The dry period of Holstein cows was between 73.34 and 82.1 days [14, 15, 22]. Koçak et al. [6] and Pelister et al. [18] reported a non-significant effect of calving season on dry period. However, Erdem et al. [14] stated a significant effect of age at calving on lactation duration. Similarly, the effect of lactation number on dry period was reported as non-significant [14, 15]. On the other hand, the effect of calving age on lactation duration was stated as significant [19]. Effects of age at calving on dry period have been reported as significant [18]. Many researchers [14, 15, 23] were found that effect of calving year on all milk yield traits (305 days milk yield, lactation duration, dry period) was significant. Inci et al. [15] reported that effects of calving year on 305 days milk yield and lactation duration were significant but non-significant on dry period. The present research work was designed to investigate non-genetics factors affecting milk yield, lactation length and dry period of Holstein cows raised under Tunisian conditions.

#### **2. Materials and methods**

The data used in the present study were taken from the Tunisian Livestock and Pasture Office (OEP). 260.241 test-day records of 5649 Holstein cows from Tunisian milk control data were analysed. Data from lactations records of cows having their first calving between 1996 and 2003 were used. To evaluate the signicant effects of calving year, season of calving, lactation number, and age at calving on different milk yield traits, eight groups for calving year were formed, between 1996 and 2003, three age groups of calving age (1) 2–4, (2) 5–6, and (3) 7 or older, four calving seasons were established; winter (December, January and February), spring (March, April and May), summer (June, July, August), and autumn (September, October and November) and five groups for parity. The 305 days milk yield was estimated from test milk yields collected once a month during all lactation periods [8, 24]. Lactations with less than five tests were not used in calculation. Milk yields were standardized to 305 days by using adjustment factors estimated by Çilek [25]. Environmental factors, which influenced lactation milk yield, lactation duration and dry period were investigated. Simple means and standard errors for the traits studied were estimated using SAS 9.13. The General Linear Model (GLM) was utilized for variance analyses of milk yield traits. Duncan's multiple range test (DMRT) was used for multiple comparisons of each trait.

The statistical model was as follows:

$$\mathbf{Y}\_{\text{ijkl}} = \mu + \mathbf{L} \mathbf{\dot{}} \mathbf{+} \mathbf{S} \mathbf{\dot{}} \mathbf{+} \mathbf{C} \mathbf{Y} \mathbf{\dot{}} \mathbf{+} \mathbf{A} \mathbf{C} \mathbf{\dot{}} \mathbf{\dot{}} \mathbf{\dot{}} \mathbf{\dot{}} \mathbf{\dot{}} \mathbf{\dot{}} \mathbf{\dot{}} \mathbf{\dot{}}$$

Where,

154 Milk Production – An Up-to-Date Overview of Animal Nutrition, Management and Health

Tunisian conditions.

**2. Materials and methods** 

duration, dry period and service period between optimal limits [6, 7]. The yields of farm animals are the result of the combined effects of genotype and environmental conditions. In order to increase the yield level, it is necessary to optimize the environmental conditions and to improve the genetic structure of the animals. In order to enhance productivity of a dairy animal, it is necessary to develop an understanding of the factors affecting its milk production. Environmental factors can be classified as factors with measurable effects (age, year, season, milking frequency, etc.) and factors with immeasurable effects (infectious diseases, parasitic infestations, etc.). The measurable effects can be determined and used in the management of the farm [8]. Environmental factors affecting variability in daily milk yield are widely documented in dairy cattle [9- 11]. The 305 days milk yield of Holstein cows was 5905 kg in Tunisia [12], 5353 kg in Morocco [13], and between 4597 and 6464 kg in Turkey [14- 16]. Environmental factors such as year of calving, season of calving and age at calving affect productivity [17]. Many researchers [6, 14] reported that the effect of calving season on 305 days milk yield was as significant and indicated that milk yield was higher in autumn and winter. Unlike, Bilgiç and Aliç [16] and Pelister et al. [18] reported that effect of calving season on 305 days milk yield was non-significant. Although, effect of lactation number on 305-days milk yield was reported [14, 15, 19] as significant. Opposing, Koçak et al. [6] and Bilgiç and Aliç [16] reported a non-significant effect of lactation number on 305 days milk yield. Effects of calving age on 305 days milk yield have been reported as significant [18, 20]. The lactation duration of Holstein cows was between 284.7 and 333.9 days in previous studies [14, 16, 21, 22]. The effect of calving season on lactation duration was reported as non-significant [6, 16, 18]. The effect of lactation number on lactation duration was reported as nonsignificant [14, 16, 19]. However, the effect of calving age on lactation duration was reported as significant [15, 18]. Zambrano et al. [23] reported that the effect of calving year on lactation duration was significant. The dry period of Holstein cows was between 73.34 and 82.1 days [14, 15, 22]. Koçak et al. [6] and Pelister et al. [18] reported a non-significant effect of calving season on dry period. However, Erdem et al. [14] stated a significant effect of age at calving on lactation duration. Similarly, the effect of lactation number on dry period was reported as non-significant [14, 15]. On the other hand, the effect of calving age on lactation duration was stated as significant [19]. Effects of age at calving on dry period have been reported as significant [18]. Many researchers [14, 15, 23] were found that effect of calving year on all milk yield traits (305 days milk yield, lactation duration, dry period) was significant. Inci et al. [15] reported that effects of calving year on 305 days milk yield and lactation duration were significant but non-significant on dry period. The present research work was designed to investigate non-genetics factors affecting milk yield, lactation length and dry period of Holstein cows raised under

The data used in the present study were taken from the Tunisian Livestock and Pasture Office (OEP). 260.241 test-day records of 5649 Holstein cows from Tunisian milk control Yijkl = Observed trait at lactation number i, calving season j, calving year k and group of age l

µ = Population mean for each trait,

Li = Effects of lactation number (i = 1, 2, 3, 4, 5),

Sj = Seasonal effects (j = spring, summer, autumn and winter),

CYk= Effect of calving year (k = years between 1996 and 2003),

ACl = Effect of group of age at calving (l= 1, 2 and 3),

eijklm = Random sampling error

## **3. Results**

The lactation performance of dairy cattle is usually measured by determining the total milk yield per lactation or per year, average daily milk yield, lactation length, lactation persistency, and milk composition. The least squares means along with their standard errors for different traits analysed are presented in table 1. The overall average 305-days milk yield was 5807.83±78.27 kg, ranging between 2271 and 7013. Average lactation length and dry period were estimated to be as 309.60±7.01 and 97.17±3.28 days, respectively when minimums were forced to be at least 127 and 11 days and when 356 and 213 days as maximums values. Average age at first calving was 1092.3 ± 196.8 days (range, 646–1588 days). The effect of year and season of calving and parity was significant (P<0.01) on milk traits. Effects of all factors (calving year, calving age, parity and calving season) on 305-days milk yield were significant (P<0.001).


**Table 1.** Records, means, standard deviations, minima and maxima of variation for milk yield, lactation length and dry period of Holstein cows

## **3.1. Sources of variation**

The major sources of variation in milk production, lactation length and dry period are genotype, environment and the interaction between the two. The influence of environmental factors on dairy production has been well documented.

#### *3.1.1. Effect of calving year*

Year of calving significantly influenced MY (P<0.001). The variation in milk yield from one year to other (Table 2) could be attributed to changes in herd size, age of the animals and good management practices introduced from year to another. The lowest 305 days milk yield (4879±117.89) was seen in 1998 years, the highest milk yield (6251±185.72 kg) was seen in 2003. Furthermore, the effects of calving year on lactation duration were statistically significant (P<0.05). Effects calving year on dry period were statistically significant (P<0.001). The dry period was lowest (96.57±5.57 days) in 2002 and highest (113.29±3.78 days) in 1996. Year wise means indicated that there was an increasing trend in lactation length from 1996 to 2003.


a-d: differences between groups with same letter in the same column are non-significant, differences with different letter are significant (p<0.05).

**Table 2.** Least square means of milk yield traits by calving year

#### *3.1.2. Effect of calving season*

The least squares analysis revealed that 305 days milk yield was significantly (P<0.001) affected by season of calving (table 3). The present results suggested that milk yield was sensitive to seasonal variation. The effect of calving season on milk yield was significant and milk yield was high (5827±69.23) in cows calving in winter. However, the effect of calving season on lactation duration was significant (P<0.001), but non-significant (P>0.05) on dry period. Then, season of calving affected both the lactation length and milk yield. As shown in table 3, least squares mean was higher for automn calvers (307.6±4.57 days) as compared to spring calvers (296.7±3.99 days). Although, summer and winter calvers have similar lactation length (301.4±4.12 and 303.7±4.28 days) but winter calvers have the highest milk yield (5827±63.17 kg). Milk yield on the other hand had the opposite trend. Summer calvers produced 614 kg less milk (5213 vs. 5827 kg) as compared to winter calvers.


a, b, c: differences between groups with same letter in the same column are non-significant, differences with different letter are significant (p<0.05).


#### *3.1.3. Effect of age at calving*

156 Milk Production – An Up-to-Date Overview of Animal Nutrition, Management and Health

length and dry period of Holstein cows

factors on dairy production has been well documented.

**Table 2.** Least square means of milk yield traits by calving year

**3.1. Sources of variation** 

*3.1.1. Effect of calving year* 

to 2003.

letter are significant (p<0.05).

*3.1.2. Effect of calving season* 

**Trait Records Means SD Minima Maxima**  305-days Milk yield (kg) 2147 5807.83 78.27 2271.53 7013.80 Lactation length (days) 1789 309.60 7.01 127.56 356.53 Dry period (days) 1789 97.17 3.28 11 213.71

**Table 1.** Records, means, standard deviations, minima and maxima of variation for milk yield, lactation

The major sources of variation in milk production, lactation length and dry period are genotype, environment and the interaction between the two. The influence of environmental

Year of calving significantly influenced MY (P<0.001). The variation in milk yield from one year to other (Table 2) could be attributed to changes in herd size, age of the animals and good management practices introduced from year to another. The lowest 305 days milk yield (4879±117.89) was seen in 1998 years, the highest milk yield (6251±185.72 kg) was seen in 2003. Furthermore, the effects of calving year on lactation duration were statistically significant (P<0.05). Effects calving year on dry period were statistically significant (P<0.001). The dry period was lowest (96.57±5.57 days) in 2002 and highest (113.29±3.78 days) in 1996. Year wise means indicated that there was an increasing trend in lactation length from 1996

**Calving year 305 days milk yield (kg) Lactation length (day) Dry period (day)** 

1147 5223±118.74b 1147 269.9±7.56a 1086 113.29±3.78a 1158 5396±127.43a 1158 273.3±9.78a 978 110.37±4.56a 2151 4879±117.89c 2151 277.6±7.67ab 1113 107.43±4.28ab 3146 5352±123.91ab 3146 281.5±7.23b 1275 103.73±5.36bc 4183 5609±127.83ad 4183 288.3±6.47b 1256 101.85±5.78c 4728 6051±156.25d 4728 292.6±8.46bc 1317 99.47±6.32dc 4689 6125±158.36d 4689 312.7±5.13c 1328 96.57±5.57d 3879 6251±185.72d 3879 322.78±6.44c 1278 98.23±4.86d a-d: differences between groups with same letter in the same column are non-significant, differences with different

The least squares analysis revealed that 305 days milk yield was significantly (P<0.001) affected by season of calving (table 3). The present results suggested that milk yield was sensitive to seasonal variation. The effect of calving season on milk yield was significant

**n Mean±SE n Mean±SE n Mean±SE** 

Total 305 days milk yields were lowest in 2-4 years of age at 5312 kg and highest in 7 years of age at 5611 kg. However, the effects of age at calving on lactation length were nonsignificant (P>0.05). Dry period increased with increase of age at calving. The lowest dry period was found in 2-4 years old age at 83.37 days and highest in 7 years old age at 99.71 days. The dry period was above the ideal value in all years. In order to make animals more profitable, it is essential they were made pregnant as soon as possible during the service period in order to shorten the dry period (Table 4).


a, b: differences between groups with same letter in the same column are non-significant, differences with different letter are significant (p<0.05).

**Table 4.** Least square means of milk yield traits by group of calving age

#### *3.1.4. Effect of parity*

The effects of parity on lactation duration were statistically significant (P<0.001). Lactation duration was shortest in lactation 5 at 297.8±3.04 days and longest in lactation 4 at 317.5±4.17 days. Lactation duration decreased with increase of lactation number. Effects of parity on


dry period were statistically significant (P<0.001). Dry period was longest in 5th lactation at 113.28±3.25 days and shortest in 3rd lactation at 87.23±2.17 days (Table 5).

a, b, c: differences between groups with same letter in the same column are non-significant, differences with different letter are significant (p<0.05).

**Table 5.** Least square means of milk yield traits by parity
