ENVIRONMENTAL FACTORS AFFECTING PREWEANING GROWTH TRAITS OF BUCHI SHEEP IN PAKISTAN

INTRODUCTION

In Pakistan, sheep is the main source of income for the rural poor especially in underdeveloped areas. In addition, sheep have an excellent export potential to earn foreign  exchange.  Buchi  is  one  of  the  important  hot- region Cholistani (desert area) sheep breeds of Pakistan with  specific  desirable  reproduction,  growth,  and  wool production  characteristics  that  need  to  be  objectively documented to be able to improve its genetic potential. Genetic improvement programs are based on exploitation of genetic variation, identification of superior animals for specific  traits  or  trait  combinations,  and  widespread utilization of these animals in a population. However, the productive and reproductive traits are also influenced by environmental factors that need to be precisely accounted for in order to estimate genetic parameters and to predict genetic values accurately. Among environmental factors, climate  and  seasonal  differences  from  year  to  year influence the production of entire flocks, while sex, type of  birth,  parity,  age  and  weight  of  dam  effect  the performance of individuals. It is necessary to precisely estimate the magnitude of these factors so that genetic variation  for  economically  important  traits  and  animal breeding values can be precisely estimated and effective genetic  improvement  plans  implemented.  Thus,  the

objectives  of  this  study  was  to  estimate  the  effect  of relevant environmental factors on birth weight, weight at about  60  days  of  age,  weaning  weight  and  weaning weight adjusted at 120 days of age.

MATERIALS AND METHODS

1.  Animals  and  data:  Preweaning  growth performance records used in this study were from a flock of Buchi sheep maintained at the Livestock Experiment Station Jugaitpir District Bahawlpur (1986-2010) Punjab, Pakistan.  This  flock  of  Buchi  sheep  started  in  1986 through purchases of 300 ewes and 6 rams. Data were recorded in loose papers and then compiled in different registers  like  birth,  live  weight,  service  and  lambing registers. Recorded information consisted of ewe, service sire,  and  lamb  identification,  date  of  birth,  birth  type, birth weight, sex, lamb weight at about 60 days of age, weaning weight, and weaning age.  There were a total of 3,564 lambs with records that were the progeny of 1,295 dams and 55 sires.  Traits were birth weight, lamb weight at about 60 days of age,  weaning  weight and  weaning weight  adjusted  to  120  days  of  age.  The  identification code for an animal was constructed by concatenating its year of birth, sex, type of birth and tag number of the animal at the farm. From the left side, the animal code

was formed by 2 to 3 digits for the year birth, 1 or 2 for sex (1 = female; 2 = male), 1 or 2 for type of birth (1 = single; 2 = twin) and the last 3 digits for the tag number of the animal at the farm. Because age at weaning varied across lambs, weaning weights were adjusted to 120 days using the following formula:

Age  of  dam  at  lambing  was  computed  as  the difference between birth dates of the lamb and that of the ewe. Keeping in mind the two breeding seasons, the year was  divided  into  two  seasons  1  and  2  (spring  and autumn). Dams were grouped into three groups each for parity, age at lambing, and weight at lambing. Dam parity groups were 1 = first and second parity, 2 = third to fifth parity, and 3 = 6 and more parities. The lambing age of dam were grouped as young (< 3.5 years), mature (3.5 to 5.5  years)  and  old  (>  5.5  years).  Weights  of  dams  at lambing were grouped as low (< 24 kg), medium (25 to 29 kg) and heavy (> 30 kg). Microsoft Excel was used for data entry and editing.

2. Farm  location,  soil,  and  climate characteristics:  The  Livestock  Experiment  Station  at Jugaitpir, District Bahawalpur was established in 1983-84 and is working under the Directorate Livestock Farms, Livestock  and  Dairy  Development  Department  Punjab, Lahore. It  is  located  at  50  km  from  Bahawalpur  on Bahawalpur-Hasalpur  road  near  Asrani  railway  station and at a distance of 340 kilometers from the provincial capital  Lahore  on  the  south-western  side  of  Punjab, Pakistan. The main purpose of the establishment of the farm was to conserve Cholistani cattle and Buchi sheep and to produce candidate bull calves and quality rams to improve the genetic potential of these breeds.  The total area of the farm is 5,200 acres. The land under cultivation is  600  acres,  while  4,555  acres  of  land  not  fit  for cultivation are used for grazing. Lastly, 45 acres are used for building and road construction.  The soil is sandy and sandy loam and it is marginally fit for cultivation. The climate is mainly dry and scanty rains may occur from July  to  September.  The  average  rainfall  is  120  mm. Temperatures in summer range from 28oC to 50oC, while winter  is  somewhat  cooler  with  temperatures  ranging from 9oC to 26oC. The cultivated area is under irrigation and the remaining area is barren rangeland. 
3. Management  and  feeding  practices: Management  and  feeding  practices  at  the  experiment station were similar across years since the introduction of Buchi  sheep.  Adult  animals  were  maintained  in  open enclosures  throughout  the  year  with  adequate  covered area to provide shade and shelter during harsh weather. Animals  were  normally  allowed  to  graze  from  7  to  9 hours  daily  except  during  harsh  weather  conditions, wherein animals were retained inside sheds. The normal practice was to allow animals to graze daily on leafy trees

and horny bushes between 5 and 6 hours and on green fodder from 2 to 3 hours daily. Animals were provided a concentrate mixture when range feed was scarce. There were two breeding seasons each year, the first one from February  16th  to  April  15th  and  the  second  one  from August 16th to October 15thaimed at getting lambs born in pleasant days and flush seasons.  Breeding females were provided a concentrate mixture 45 days before breeding for flushing and 60 days after parturition at a rate of 250 to 500 grams per ewe. Breeding rams were also offered a concentrate mixture at the rate of 500-750 grams during breeding. Young lambs  were mostly kept indoors  until one  month  of  age.  The  lambs  were  allowed  to  suckle freely  through night  until the  ewes  were taken out  for grazing  in  the  morning.  After  one  month  of  age,  the lambs remained  with their mothers for 24 hours up to weaning. The weaned lambs were shifted to separate pens for  post-weaning  rearing.  The  feeding  regime  was reported to have been similar throughout the years of the study,  with  some  variation  from  time  to  time  due  to climate and shortage of fodders and concentrate during scarce  periods.  Animals  were  vaccinated  against enterotoxaemia, foot and mouth disease, sheep pox and pleura-pneumonia.  Drenching  with  anthelmintic  drugs against internal parasites was routinely done every four months and dipping against external parasites was carried out twice a year.

4. Statistical  analysis:  Data  were  analyzed  to estimate the effect of lamb year and season of birth, sex, type of birth, parity, age of dam at lambing, and weight of dams at lambing on 4 preweaning traits:  birth weight, weight  at  about  60  days  of  age,  weaning  weight  and weaning weight adjusted to 120 days of age.

The mathematical model used to analyze the 4 preweaning traits can be written as follows:

Yijklmnp=  μ +  yobi  + sobj  + sexk  + tobl  + dalcm  + dwlcn + parityp+ (yob*sob)ij + (yob*sex)ik+ (sob*sex)jk + (sob*tob)jl + (sex*tob)

Where

Yijklmnp= observation on a trait

μ = population mean

yobi=year of birth

sobj= season of birth

sexk= sex of lamb

tobl= type of birth

dalcm= age of dam at lambing 

dwlcn=  weight of dam at lambing

Parityp= dam parity group

(yob*sob)ij=  interaction between  year and season of birth (yob*sex)ik=  interaction between  year of birth and sex of lamb (sob*sex)jk =  interaction between  season of birth and sex of lamb

(sob*tob)jl =  interaction between  season and type of birth (sex*tob)kl  =  interaction between  sex of lamb and type of birth eijklmnp  =  random  residual  associated  with  each observation with the assumption that it was normally and independently distributed with mean zero and variance σ2

Data  were  analyzed  using  the  mixed  procedure  of  the Statistical Analysis System (SAS, 2011).

RESULTS AND DISCUSSION

Data  description:  Means  ±  SE,  standard  deviations, minimum  and  maximum  values  for  the  4  preweaning growth traits are presented in Table 1. The means ± SE were 2.84 ± 0.009 kg for birth weight, 7.64 ± 0.01 kg for weight at around 60 days of age, 12.64 ± 0.02 kg for weaning weight and 12.55 ± 0.03 kg for weaning weight adjusted to 120 days of age. The percentage of single and twin births were 96 and 4 percent, respectively. The sex ratio was 52:48 for males and females.

Environmental  factors  affecting  growth  traits: Estimates of environmental factors for the 4 pre-weaning growth  traits  are  presented  in  Table  2  and  discussed below one trait at a time. 

1. Birth  weight:  The  analysis  of  variance  to evaluate the influence of different environmental sources of  variation  and  interactions  between  these  factors  on birth weight is presented in Table 2. Significant effects were  obtained  for  year  of  birth  (P<0.0001),  season  of birth (P<0.0008), sex of lamb (P<0.0004), type of birth (P<0.0001) and dam parity group (P <0.0497) on birth weight of lamb, while the effects of age and weight of the dam  at  lambing  on  birth  weight  were  non-significant. There was also a significant interaction between the year and season of birth (P<0.0001), and between year of birth and sex of lamb (P<0.0001).The significant influence of year,  season,  sex  of  lamb  and  type  of  birth  on  birth weight  of  lamb  obtained  here  was  in  agreement  with results  from  previous  studies  in  Pakistan  in  different breeds of sheep (Hissardale, Lohi, Thalli, Mengali and Kajli)  kept  at  different  locations  and  management conditions.(Akhter  et  al.,  2001;  Babar  et  al.,  2004; Hussain;  2006;  Iram;  2008;  Tariq  et  al.,  2010; Farmanullah et al., 2011).The findings of Qureshi et al., (2010) for Kajli and Kakar et al. (2011) for Balochi and Bibrik breeds of sheep were slightly different. In these studies, birth weight was significantly influenced by year of birth, age of dam, sex and birth type. However, the effect  of  season  on  birth  weight  was  non-significant. Results from studies conducted in other countries were also in agreement those here. Cloete et al. (1998), Dixit et al.  (2001),  Mendal  et  al.(2003),  Selvaggi  et  al.(2011), Thiruvenkadan (2011) and Petrovic et al. (2011) reported that  year and season of lambing, sex of lamb, type of birth,  and  age  of  dam  were  significant  sources  of variation for lamb birth weight in Dhone Merino, Bharat Merino, Muzarnagri, Pulgia, Mecheri and in two Serbian breeds of sheep (Pirot and Svrlijig).The non-significant effect of age of dam on birth weight found here differed from findings in these studies. Similarly, in most of the referenced  studies  the  interaction  between  year  and

season of birth, and the interaction between year of birth and  sex  of  lamb  were  not  estimated.  A  significant interaction between year and season of birth existed here for  birth  weight  of  lamb.  This  indicated  that  seasons (spring and autumn) were not the same across years, thus different  estimates  were  obtained  for  different combinations  of  years  and  seasons  for  this  trait.  Least squares means for year-season interactions ranged from 2.036 ± 0.061 kg in the spring of 1997 to 3.179 ± 0.08 kg in autumn of 1996. However, Tariq et al. (2010) reported a non-significant interaction between year and season of birth  for  birth  weight  in  Mengali  lambs  in  Pakistan. Similarly, the significant interaction between year of birth and sex of lamb found in the present study indicated that these  two  factors  were  not  independent  and  that  sex effects  differed  across  the  years.  Matica  et  al.  (2003) reported  non-significant  interactions  between  year  of birth and sex of lamb for birth weight in Sabi sheep in Zimbabwe.  Least  squares  means  for  the  interaction between year of birth and sex of lamb ranged from 2.000 ± 0.155 kg (females born in 1986) to 3.011 ± 0.061 kg (males  born  in  1998).  Figure  1  shows  a  graphical representation of fluctuations in least squares means for birth  weight  across  years  for  the  spring  and  autumn seasons. Similarly,  Figure  2  shows  changes  in  least squares means for birth weight  from 1986 to 2010 for male and female lambs.

The non-significant interaction between sex and birth type was in agreement with the findings of Hussain (2006),  Iram  (2008)  and  Farmanullah  (2011),  but significant interactions of season with sex and birth type differed from results obtained by Hussain (2006) in Thalli sheep. The significant effect of birth type on birth weight estimated here was in agreement with all the referenced studies.  This  indicated  that  single  born  lambs  were heavier than twin born lambs as they likely received more nutrients  in  the  womb  of  their  dams  than  twin  born lambs.  The difference between least squares means for single and twin born lambs was 0.451 ± 0.043 kg. The significant  estimate  of  dam  parity  group  for  this  trait indicated that lambs born in parities 3 to 5 were heavier than  lambs  born  in  parities  1  and  2andlambs  born  in parity 6 and later were heavier than lambs born in parities 1  to  5.  Mendal  (2003),  Gbangboche  et  al.  (2006)  and Thiruvenkadan  (2011)  also  reported  that  lambs  from ewes of 3rd and 4th parities were heavier than lambs out of parity 1 and 2 ewes in Muzaffernagri, Djallonkeand Mecheri  breeds  of  sheep.  BelaandHaile  (2009)  also reported  parity  to  be  a  source  of  variation  in  different breeds of sheep in Ethiopia for birth weight.  The least squares  means  difference  between  dam  parity  group  1 and 2 in the present study was 0.066 ± 0.0466 kg whereas differences  in  least  squares  mean  between  dam  parity group  3 and dam parity  groups  2 and 1  were  0.047 ± 0.042 and 0.018 ± 0.038 kg, respectively. This indicated that  young  ewes  tended  to  produce  lighter  lambs  as

compared  to  matured  and  older  dams  which  may  be attributed to the larger size of the uterus as ewes grew older.  Mature  ewes  after  attaining  full  growth  and development  could  allocate  more  nutrients  to  the nourishment of lambs in the uterus than immature ewes. Younger  ewes  likely  utilized  a  large  fraction  of  the ingested nutrients for their own growth and development and  consequently  produced  lambs  of  smaller  birth weights than older ewes. 

2. Weight at about 60 days of age: The analysis of  variance  to  evaluate  the  influences  of  different environmental  sources  of  variation  and  interactions between  these  factors  on  weight  of  lamb  at  around60 days of age is presented in the Table 2. Year of birth (P< 0.0001) and sex of lamb (P<0.0113) affected this trait.  Season and type of birth, parity, age and weight of the dam  at  lambing  were  non-significant.  However, significant interactions existed between year and season of birth (P <0.0001), and between the year of birth and sex of lamb (P<0.0001). Similar results were reported at various locations in different sheep breeds of same type. Akhtar et al. (2001), Matica et al. (2003) and Hussain (2006)  reported  that  year  of  birth  and  sex  of  were significant sources of variation for lamb weight at about 60 days of age in Hissardale, Sabi and Thalli breeds of sheep.  In  addition,  these  authors  reported  significant season, type of birth and age of dam effects that were non-significant  in  this  study.  Similarly,  Dixit  et  al.  (2001), Borg et al. (2009), Selvaggi et al.  (2011) found significant effects for year of birth and sex of lamb as well as birth type weights around 90, 45, and 30 days in Baharet Merino, Western Range sheep and Pulgia lamb. The non-significant effect of birth type here may have been largely due to the low percentage of twins (4%) in

the Buchi population here.

Significant interactions between year and season of  birth  were  found  here.  This  indicated  that  seasons (spring and autumn) were not the same across the years and  different  effects  were  obtained  with  different combination of the years and seasons on this trait. Least squares means for year-season interactions ranged from 6.887 ± 0.124kg (autumn of 2006) to 8.249 ± 0.083kg (spring  of  1994).  Similarly,  the  significant  interaction between  year  of  birth  and  sex  of  lamb  found  here indicated that these two factors were not independent and that sex effects differed across the years.  However the finding  in  Sabi  sheep  was  different  and  Matica  et  al. (2003)  reported  non-significant  interaction  between  the year of birth and sex of lamb. Least squares means for the interaction between  year and sex ranged  from  6.941 ± 0.096 kg(males born in 2006) to 8.278 ± 0.106 kg (males born  in  1990).  Hussain  (2006)  also  obtained  a  non- significant  interaction  between  sex  and  birth  type  in Thalli  sheep,  and  contrary  to  results  here,  he  reported significant interactions between seasons and sex and birth

type.  Figure 3 presents trends in least squares means for lamb weight at around 60 days of age by seasons across years from 1986 to 2010.  In addition, Figure 4 depicts the  trends  in  least  squares  means  for  lamb  weight  at around 60 days of age by sex from 1986 to 2010.

3. Weaning  weight:  The  analysis  of  variance  to evaluate the influences of different environmental sources of  variation  and  interactions  between  these  factors  on weaning  weight  is  presented  in  the  Table4.  The  only significant main effect (P < 0.0001) was year of birth. The  interactions  between  year  and  season  of  birth, between year of birth and sex and between season of birth and  sex  were  also  significant  (P  <  0.001).  All  other effects in the model were non-significant. The significant influence of year of birth and sex of lamb on weaning weight obtained here was in agreement with results from previous  studies  in  different  breeds  of  sheep  (Dhone Merino,  Hissardale,  Muzafernagri,  Lohi,  Kajli,  Balochi and Bibrik) kept at different locations and under various management conditions.(Cloete et al; 1998 ; Akhter et al., 2001;  Mendal et al., 2003;  Babar et al., 2004; Iram; 2008;  Qureshi et al., 2010; Farmanullaha., 2011; Kakar et  al.  2011).However,  contrary  to  results  here,  most referenced studies found significant season of birth, birth type and age of dam effects. Similarly, Mendel (2003) and Thiruvenkadan (2011) in Muzaffernagri and Mecheri breeds of sheep in India found significant parity effects as opposed to the non-significance of group parity effects here. Lack of birth type effects for weaning weight may be related to the low percentage of twin births (4%) in this dataset. The non-significant attraction between sex and birth type was also in agreement with results from Iram  (2008)  in  Lohi  sheep.  A  significant  interaction between  year  and  season  of  birth  existed  for  weaning weight.  This  indicated  that  the  seasons  (spring  and autumn) were not the same across the years and different effect were observed by the different combination of the years and seasons on this trait. Least squares means for year-season interaction ranged from 11.053 ± 0.186 kg in the spring of 2004 to 14.098 ± 0.269  kg in autumn of 1996. Similarly, the significant interaction between year of birth and sex indicated that these two factors were not independent and that sex effects differed across the years. The least squares means between interactions of season of birth and sex of lamb ranged from 12.652 ± 0.115 kg (females born in spring) to 12.74 ± 0.115 kg (males born in  spring)  for  this  trait.  Two-way  Interactions  among other factors in the model here were unavailable in other studies, thus comparisons could not be made. Trends for least squares means for weaning weights by year of birth and season combinations are shown in Figure 5, and by

year of birth and sex of lamb combinations in Figure 6.

4. Weaning weight adjusted to 120 days of age: The  analysis  of  variance  to  evaluate  the  influences  of different  environmental  sources  of  variation  and

interactions  between  these  factors  on  weaning  weight adjusted to 120 days of age is presented in the Table5. Year  of  birth  (P<0.0001)  and  sex  of  lamb  (P<0.0165) were  important  effects  for  this  trait.  In  addition, significant interactions existed between year and season of  birth  (P  <  0.0001),  between  year  of  birth  and  sex (P<0.0001), between season of birth and sex of the lamb (P<0.0001) and between season of birth and type of birth (P <0.0427).  The significant influence of  year of birth and  sex  of  lamb  obtained  here  was  in  agreement  with results of previous studies at various locations in different breeds of sheep. Hussain (2006)and Tariq et al. (2010) in Thalli and Mangali breeds of sheep in Pakistan, Ceyhan  et al. (2009) and Ozdaret al. (2009) in Sakiz and Turkish Merino breeds of sheep in Turkey and Borg et al. (2009) in Western Rang sheep in USA reported that year of birth and sex of lamb were significant sources of variation for weaning  weight  adjusted  to  120  days  of  age.  In  Iran, Kesbi et al. (2007), Rashidi et al. (2008) and Lawf and Noshery  (2008)  also  reported  the  similar  results  in Kermani, Mehrban and Lori breeds of sheep. However

these  referenced  studies  reported  significant  effects  of season of birth, type of birth and age of dam for this trait which contrary to results here. 

Results  here  also  showed  significant  year  of birth by season of birth interactions.  This indicated that the seasons (spring and autumn) were not the same across years,  thus  year-season  combination  estimates  differed over time. Saghi et al. (2007) reported similar results in Baluchi  sheep  in  Iran.  Least  squares  means  for  year- season  combinations  ranged  from  10.745  ±  0.218  kg (spring of 2004) to 14.565 ± 0.309 kg (autumn of 1996). Similarly, the significant interaction between year of birth and  sex  of  lamb  found  here  indicated  that  these  two factors were not independent and that sex effects differed across the years. Least squares means for the interaction between  year  and  sex  ranged  from  10.86  ±  0.192  kg (males born in 2007) to 14.415 ± 0.291 kg (females born in  1996).  Trends  for  least  squares  means  for  weaning weights adjusted to 120 days of age by year of birth and season combinations are shown in Figure 7, and by year of birth and sex of lamb combinations in Figure 8.

Table 1. Statistical description for preweaning growth traits in Buchi sheep1

Traits  No.  Mean ± SE  SD  Min.  Max. Birth weight (kg)  3564  2.84± 0. 009  0.515  1.5  4.5 Weight at about 60 days of age (kg)  3496  7.64 ± 0.014  0.829  4  10 Weaning weight (kg)  3349  12.64 ± 0.03  1.682  8  19 Weaning weight adjusted to 120 days of age (kg)  3349  12.55 ± 0.03  1.946  6  20 1SE = Standard error; SD= Standard Deviation.

Table 2. Significance level and F values for weight at different ages in Buchi Sheep

Effect  DF  Birth  Around 60 days  Weaning  120 Days Year of birth (yob)  24  17.08** 24.34** 22.20** 29.78** Season of birth (sob)  1  11.28** 2.1  0.08  0.00 Sex of lamb(sex)  1  12.45** 6.42*  1.90  5.75* Type of birth( tob)  1  106.18** 1.59  0.60  2.43

Dam age at lambing (dalc)  2  0.78  0.67  0.25  0.84 Dam weight at lambing (dwlc)  2  0.31  0.61  0.15  0.97 Parity  2  3.00*  1.28  0.84  1.23 Age of lamb  2  -  0.27  0.47  - yob*sob  23  11.61** 2.77** 1.18  6.89** yob*sex  23  5.53** 7.96** 6.60** 7.45** sob*sex  1  0.87  3.21  8.75** 10.91** sob*tob  1  0.46  3.29  10.46** 4.11* sex*tob  1  0.66  2.11  0.90  0.02 DF= degrees of freedom; * = Significant (P < 0.05); ** = Significant (P < 0.01).

The  significant  interaction  between  season  of  to 12.638 ± 0.132 kg for females also born in the spring birth and sex was in agreement with results from Hussain  season.  Similarly,  the  significant  interaction  between (2006). This indicated that the sex effect was not same  season and type of birth indicated that the type of birth across  the  seasons.  The  least  squares  means  for  effect was not same across the seasons. Hussain (2006) interactions  between  season  of  birth  and  sex  of  lamb  also reported a significant interaction between these two ranged from 12.447 ± 0.131 kg for males born in spring  factors. The difference of least squares means revealed

that the single lambs born in autumn were 0.619 ± 296 kg heavier  than  twin  lambs  born  in  the  same  season.  However, twins born in the spring season were0.079 ± 174  kg  heavier  than  singles  born  in  the  same  season. Hussain (2006) also reported non-significant interactions between  sex  and  type  of  birth  in  Thalli  sheep  in agreement with results here.

Figure  1.  Least  squares  means  for  birth  weight  by

year-season combination

Figure  2.  Least  squares  means  for  birth  weight  by

year-sex combination

Figure  3.  Least  squares  means  for  lamb  weight  at

around 60 days of age by year of birth-season combination

Figure  4.  Least  squares  means  for  lamb  weight  at

around 60 days of age by year of birth-sex combination

Figure 5.  Least squares means for weaning weight by year of birth-season combination

Figure 6.  Least squares means for weaning weight by year of birth-sex combination

Figure  7.  Least  squares  means  for  weaning  weight

adjusted to 120 days of age by year of birth-

season combination

Figure  8.  Least  squares  means  for  weaning  weight

adjusted to 120 days of age by year of birth- sex combination

Conclusions:  The  variation  in  least  squares  means  for preweaning  traits  in  Buchi  sheep  across  years  due  to interactions between year of birth, season of birth, sex of lamb and type of birth found here may have been due to the  combined  effects  of  climate  (e.g.,  temperature  and humidity), feeding conditions (e.g., type and availability of  feed),  and  sheep  management  influenced  by  staff training  and  availability.  To  maintain  a  reasonably productive and profitable sheep production system with Buchi sheep, feeding and management would need to be flexible  to  effectively  respond  to  changes  in  type  and availability of range feed with climate fluctuations.

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