Lactation specific and life time demographic parameters in a Holstein Friesian herd in the central highlands of Ethiopia

Gebeyehu Goshu and Harpal Singh

Addis Ababa University, College of Veterinary Medicine and Agriculture,
P.O. Box 34, Debre Zeit, Ethiopia
ggoshu2000@yahoo.com

Abstract

The study was made to estimate the lactation specific and life time demographic parameters from the records of 901 Holstein Friesian cows born in the period of 1985 to 2008 at Holeta Bull Dam Station, Ethiopia.

The probability of a cow being lost from herd was 0.263 during the first lactation and the rate increased with lactation. Survival rate in the herd during first lactation was estimated at 0.738 and the rate increased during first three lactations and there after declined at an inconsistent rate. Stayability in the farm was maximum (0.737) for cows in first lactation, and continuously decreased with lactation number. Cows had expected herd life of 2.457 lactations at the first lactation and thereafter the estimate continued to decline. The probability of producing a live female calf by a cow at her first lactation was 0.481 and approached the expected sex ratio of 50:50 at the 4^th and 5^th lactations. The reproductive value of cows was maximum at the first lactation and all other lactations had less than one. Older cows had lower reproductive value. The mean lactations of cows present and lost from the herd were in average 3.49 and 4.35 lactations, respectively indicating that cows present in the farm were younger. The probability of a cow being lost from the herd and life expectancy at birth was as 0.32 and 1.28 lactations, respectively. The net reproductive rate for the herd was 1.50 indicating that each cow produced on an average 1.5 female calves.  Improvement in most lactation specific and population parameters can be obtained by reducing forced culling and mortality at early age through better nutrition and reproductive health management.  

Key words: demography, milk production, population, probability

Introduction

Demographic analysis of life time parameters such as reproduction and mortality rates, growth in numbers and biomass, age structure, sex ratio, and average longevity is one method to characterize livestock populations. Results of such analyses have been used in livestock to formulate strategies for culling and replacement, organize breeding scheme and as a check on management practices (Greer et al 1980; Schones et al 1985; Ahmed et al, 1992). Age distribution and herd life expectancy are of primary interest in dairy cattle production. Knowledge of life expectancy for cows at a given age is needed to plan mating for perspective bull calves and to determine culling policies (Andrus et al 1969). Sex ratio is very important statistics in dairy cattle production in that dairy farmers seek female dairy calves to maintain their herd. Furthermore, the requirement for lower sex ratio in dairy cattle is increased when replacement rates are high (Berry and Cromie, 2006). The objective of the study was, therefore, to estimate lactation specific and overall life time demographic parameters in a Holstein Friesian herd at Holeta Bull Dam Station, Ethiopia. 

Materials and methods

Study area

Holeta Cattle Genetic Improvement Center is located 33 km west of Addis Ababa, in West Shoa Zone of Oromia Regional state. The center lies at longitude 38º 30' E and latitude 9º 3' N and at about 2400 meters above sea level. The site is characterized by cool sub-tropical climate with mean maximum and minimum temperatures of 22.3ºC and 6.16ºC, respectively with mean relative humidity of 59%. The mean annual rainfall ranged from 818 to 1247 mm with an average of 1014 mm (HARC, 2008).  

Animal management

Milking cows allowed to graze on native pasture from 8:00 am to 3:00 pm and supplied with native grass hay and green vetches (Vicia dasycarpa) on return to the barn. Milking cows were grouped according to their milk production classes as high (>14 liters), medium (8 to 14 liters) and low (< 8 liters) yielding and each milking cow is provided with additional 0.5 kg concentrate per liter of milk, while pregnant dry cows are supplied with 3 kg of concentrates in the last two months of pregnancy. The concentrate mix was composed of 30% wheat middling, 30% noug seed cake (Guizeta abysinica), 25% wheat bran, 10% corn, 4% limestone and 1% salt. Calves were fed colostrums immediately after birth and thereafter allowed to consume 490 liters of milk before weaning at the age of 120 days. All animals had free access to water.

Most of the cows were served at first observed heat after calving. Heat detections were routinely followed three times in a day, i.e. early in the morning after milking; in the resting period in midday; and in the afternoon before milking. Regular vaccinations against contagious bovine pleura-pneumonia, lumpy skin disease, anthrax, and blackleg, foot and mouth disease and pasteurellosis were given and treatments provided when incidence of cases observed. Culling was practiced as a result of fertility failures, chronic mastitis, tuberculosis, old ages and low daily milk production (Birhanu, 2009). 

Data source, definition of parameters and anlyses

Lactation records of 901 Holstein Friesian cows born in the farm from 1985 to 2008 were used in the analyses. Only cows that had records of birth, calving, dry off and disposal (culling and mortality) dates were considered. Life table was constructed on the basis of lactation from parity one to twelve.

Lactation specific parameters included in the study were loss rate, survival rate, survivorship, life expectancy, sex ratio, reproductive value and lactation specific herd structure.

Loss rate (Q_x): it is the probability of a cow, assuming survival to lactation x, of dying or culling before lactation x+1. Thus,

Q_x=d_x/n_x

Where,

d_x is the number of animals died or culled during lactation x;

n_x is the number of animals present in the herd at the beginning of lactation x.

Survival rate (P_x): is the complement of Q_x. It is the probability of a cow assuming survival to lactation x, of surviving to lactation x+1. 

P_x= L_x + 1/L_x = 1- Q_x

Where  L_x is stayability  of a cow  to lactation x

Thus it is the probability of an animal being present to lactation x in the herd to the next lactation x+1.

Survivorship or Stayability (L_x): the probability of a cow at first lactation present in the herd to lactation x and estimated as number present at lactation x divided by the number alive at first lactation. The survivorship at first lactation was taken as unity and hence, L₀=1.0. The L_x= n_x/n₀, this can also be estimated as:

L_x=P_x.L_x-1

where,

n_x is the number of survivors at lactation x

n₀ is the number of cows at first lactation

Expected herd life (E_x): it was estimated as the sum of probability of an animal of a given lactation remaining in the herd (P_x) through each succeeding lactation up to the last lactation. Thus, average life expectancy is estimated as per Ahmed et al (1992):

E_x= P_x+ P_x.P_x+1 + P_x.P_x+1.P_x+2…..+P_x.P_x+1.P_x+n       

Lactation (age) specific birth rate (M_x): is the probability of a cow of lactation x producing a live female calf and estimated as the ratio of number of calves produced by cows of lactation x to number of cows in lactation x

Reproductive value (V_x): is the relative contribution of a cow of lactation X to future generation and estimated as

Vx =

Mean rate of loss per female per lactation ( _{QUOTE x}): it is the average probability of a female animal being lost from the herd each lactation and was calculated as per Caughley (1966) formula: 

                                                              Per female per year

Mean lactation of cows being lost (death and culling): this parameter was calculated by multiplying each lactation (x) by proportion of cows lost from the herd (q_x) and adding the products i.e.,               

     (Greer et al 1980)

Mean lactation of cows present in the herd: this parameter was estimated by multiplying each lactation (L_x) by proportion of total cows present in the herd (p_x) and adding the product i.e., _QUOTE

                                                             (Greer et al 1980)

Net reproductive rate (NRR): expected number of daughters produced by each animal entering the population or finite rate of population increase per generation is known as net reproductive rate. This was estimated as according to Schons et al (1985)

                                                 NRR= QUOTE

Generation interval (T): this is the mean interval between birth of a parent and birth of its offspring and estimated according to Schons et al (1985) as follows

                                                            T =

Specific probabilities and population parameters were estimated from the tabulated data using the routine procedures of SAS (2002).

Results

Lactation specific parameters

Lactation specific demographic parameters were depicted in Table 1. The probability of a cow being lost from herd (Q_x) was 0.263 during the first lactation. This probability of depletion was almost same during the 2^nd and 3^rd lactations but increased continuously from 4^th lactation (about 1/3^rd) to 12^th lactation when almost 2/3^rd of the cows lost from the herd.

Further, it was also observed that about 71% of the total cows left the herd by the end of fourth lactation and only about 29 % of cows remained to produce their progeny in the herd. The probability of survival rate (P_x) in the herd during first lactation was estimated at 0.738 and the rate increased during the first three lactations and there after declined at an inconsistent rate till it reached to its lowest of 0.333 in the 12^th lactation. Stayability (L_x) in the farm was maximum (0.737) for cows in first lactation, and continuously decreased in order of increased lactation number.

The lactation specific expected herd life (E_x) of cows present in the herd was maximum during the first lactation and thereafter the estimate decreased with the increase in the lactation. The probability of producing a live female calf (M_x) by a cow at her first lactation was as 0.481 and approached the expected sex ratio of 1:1 in the mid lactations. The lactation specific reproductive value (V_x) of cows was highest in the 1^st lactation and all other lactations had less than one. The lowest value was observed for the 8^th and 9^th lactations indicating that older cows had lower reproductive value than that of replacement heifers and younger cows.

Population parameters

The life time demographic parameters were presented in Table 2. The mean lactations of cows present were higher than the average of cows present in the farm. About 32% cows per lactation were lost because of mortality and culling. On the average each cow produced more than one calf.

Discussion

Lactation specific parameters

The findings of females being lost (Q_x) during the first lactation in the Holeta herd were in conformity with the reports of Nieuwhof et al (1989), Gadzhiev et al (1991), Tomar et al (1994), Lathwal et al (1995), Tomar et al (1996) for various Zebu and crossbred cows. The observed probability of lactation specific survival rate (P_x) in Holstein Friesian generally low, which could be due to stringent culling and high mortality rates. Berhanu et al (2011) reported a culling of 603 cows due to various diseases in the same herd during the period of 1987 to 2008 (21 years). The survival rate for 1^st lactation is closer to the values reported by Lathwal et al (1995) for Red Sindhi cattle breeds. Tomar et al (1994, 1996) estimated a higher survival rate of 0.78 and 0.78 at first lactation for Sahiwal and Tharparkar, respectively. The highest survival rates were observed for second and third lactations and thereafter there was a declining pattern. Similar pattern of declining survival rate were reported by Lathwas et al (1995), Tomar et al (1996) and Atrey et al (1995) 

Cows in the present study were stayed lower period of time than that reported by Tomar et al (1994), Lathwal et al (1995) and Tomar et al (1996) for Sahiwal, Red Sindhi and Tharparkar breeds in first lactation, respectively. Similarly, Lucia and Jazmin (2002) after studying the stayability of 11 herds composed of Bos taurus × Bos indicus crossbred cows reported that out of 1785 cows 72%, 56% and 43% survived to 2nd, 3rd and 4th calving, respectively. The loss rate was increased with the increased of lactation number. Stayability of dairy cows in the tropics was affected by the level of exotic inheritance and pure and grade Friesian cows had less effective herd life which ultimately affect the replacement rate of the herd. Lemose et al (1996) compared six Holstein Friesian×Guzera crosses (1/4, 1/2, 5/8, 3/4, 7/8 and 31/32 Holstein Friesian) on different management levels and mortality increased as the level increased from ½ to 15/16. Moreover, Gebeyehu (2005) reported that the breeding efficiency declines for grade Friesian cows.

Lower stayability in this study could be attributed to high culling and death rate of cows.

Expected herd life (E_x) is a function of survival rate at each lactation which in turn may be influenced by disease prevention and feeding management condition of the farm. The present finding is comparable to the findings of Lathwal et al (1995). Higher estimates of 2.72 and 2.82 lactations of E_x than the present study were reported for Sahiwal (Tomar et al 1994) and Tharparkar (Tomar et al 1996) cattle, respectively.

The estimates of lactation specific female birth rates revealed that the probability of producing female calf was not in conformity of the expected 1:1 ratio (Table 1). Studies indicated that sex ratio is affected by the type of services, place of deposition of semen, and time of insemination. Berry and Cromie (2006) studied the effect of artificial insemination and natural mating on sex ratio of Holstein Friesian and other breeds and reported that AI increased the likelihood of male calf by 1.04 to 1.08 times. Furthermore, Xu et al (2000) reported that frozen semen resulted in 1.24-1.66% units more male. At Holeta farm, the artificial insemination service was based on frozen semen collected from imported Holstein Friesian bulls and young male calves selected from those bull calves born at the farm. This might affect the capacitating ability of X-chromosome bearing sperm cells. Moreover, the usual practice of deposition of semen was in the body of uterus and might favor male calf births. Zobel et al (2011) investigated effects of different semen deposition sites on the sex ratio of Simmentals cattle and concluded that intra cornual semen deposition resulted in a higher ratio of female calves whereas uterine body deposition site resulted in higher male calf ratio. Moreover, the time of artificial insemination appeared to affect gender of calf. Richard et al (1998) studied the sex ratio of dairy cows which were inseminated at 0, 8, 16, and 24 and 32 hours after second injection of GnRH and found that cows bred at 0 and 32 hours had a higher percentage of female offspring. The amount of weight body lost between calving and conception and the rate of loss affected the sex of resultant offspring. Less weight loss or greater weight gain between calving and conception was associated with greater likelihood of a male calf. This was supported by the findings of Roche et al (2006) who reported that the birth of a bull calf was 1.85 times more likely in cows that lost no body condition score from calving to conception. Although concurrent records were not available the present finding suggests the necessity of monitoring the body condition of dairy cows at different physiological stage. The present sex ratio in first parity was closer to the findings of Silva et al (2007) who reported calf sex ratio of 53.3% male and 46.7% female for singleton in Friesian cows. The values for lactation ten and beyond are much higher than the lower lactations and this could be due to the effect of small sample size.

Dairy cows replacement rate was not only affected by female calf sex ratio. Reproduction wastage and calf mortality also contributed to the low rate. A range of perinatal mortality from 0.2 to 26.4% in Holstein calves reported by Silva et al (2007) confirms the above statement. Moreover, they estimated an increased calf mortality from 9.0 to 11.7% for nulliparous; from 4.4 to 4.8% for primiparous and from 4.9 to 5.6% during 1996 to 2004 and the rate was proportional to the size of the herd. Similarly, Fuerst-Waltl and Sørensen (2010) noted that about 9.4% of calf mortality from day one to before first calving in Danish Holstein herd. These findings suggest that calf management is still important area to keep the herd size. Dairy production in tropical countries like Ethiopia is influenced by poor adaptation of exotic breeds and high calf mortality. After studying the dynamics of Friesian herds in four dairy farms Menjo et al (2009) concluded that 25% of the Holstein Friesian cattle born on the Kenyan large scale farms were lost before reaching to a productive age, indicating the limitations of such animals’ adaptability to the prevailing environmental conditions. Moreover, Moran (2011) reviewed 17 studies documented on mortality of calves in Asia, tropical Africa and south America and summarized that pre-weaning calf mortality ranged from 15 to 25% and often as high as 50%. The main reasons attributed to the death of exotic breeds in these countries were poor adaptation coupled with poor health, feeding and management problems. Improved management strategies leading to lower calving interval, higher calving rate, reduced still birth and pre-weaned calf mortalities and fewer non pregnant heifers can supply many more dairy herd replacements. Such strategies can increase the number of replacements heifer calves in the herd from 15 to 35%, thus allowing farmers to increase the herd size through natural increase. Higher female calve births at the older ages in the current study was different from the finding of Berry and Cromie (2006) who noted that the probability of a male calf being born was higher in older cows compared to younger cows. However, Yilmaz et al (2010) reported that management, calving year/season, parity and sire had no effect on the sex ratio of the calves.

Reproductive value is the function of current (female birth rate) and future female calve births. The reproductive value at first lactation for the current study is lower than the findings of 1.86 (Tomar et al 1996). They also showed that older cows had a reproductive value of less than1.0 after 9^th lactations.

Population parameters

The mean number lactations accomplished by cows present in the herd were comparable with that reported by Tomar et al (1994) for Sahiwal. However, the present average was higher than those reported by Lathwal et al (1995) in Red Sindhi, but lower than the reports of Tomar et al (1996) in Tharparkar breeds. The estimate for cows lost from the  herd was very close to that reported by Tomar et al (1994), Lathwal et al (1995), Tomar et al (1996) and Atrey et al (2005). The present higher estimate showed that cows in Holeta herd were comparatively older at the time of their replacement than other herds. The variations in observations of different workers could be due to the difference in availability of replacement heifers in different herds. The average probability of a cow being lost from the herd showed that 32.0 % of the cows were being lost either due to death or culling from the herd per lactation. However, the present observed rate of cow loss was lower than that reported by Atrey et al (2005) for Frieswal cattle (0.52 per lactation).

Higher net reproductive rate than the present study were reported by Tomar et al (1994) for Sahiwal (1.78), Lathwal et al (1995) for Red Sindhi (1.60), Tomar et al (1996) for Tharparkar (1.79), while Atrey et al (2005) observed lower net reproductive rate (0.96) for Frieswal crossbred cows. The average generation interval in  the Holeta herd was lower than Danchin-Burge et al (2012) for Holstein Friesian (5.6 years) but higher than the reports of Atreyet al (2005) for Frieswal (2.54 years) herds.

Conclusions

• Survival rate and stayability decreased with the accompanied increase of loss rate as parity number increased.

  
  

• Cows were lost from the farm due to mortality and culling at a rate of 32% per lactation. 

  
  

• It is essential to improve feeding condition of cows and calves along with reproductive health management to reduce culling and mortality of female calves at early ages.

Acknowledgments

The authors would like to thank the National Artificial Insemination Centre for allowing us to use the data. We pay special thanks to the management unit and experts of the Holeta station for collaborating in data collection.  

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Received 21 August 2013; Accepted 10 October 2013; Published 1 November 2013

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