milk is the major source of income generated on dairy farms , and over the past several decades , milk production by dairy cows has increased markedly .
however , this improvement comes at the cost of higher incidences of reproductive health problems and reduced fertility .
large energy requirements at the onset of lactation in high - producing dairy cows results in a severe negative energy balance during the early lactation period , which may adversely impact postpartum health and fertility . as a result of milk production quotas , reductions in production costs can allow dairy farms to maintain profitability .
for example , the costs associated with raising replacement heifers have been estimated to be approximately 20% of the overall dairy herd operating cost . moreover , involuntary culling is caused mainly by reproductive failure .
thus , more attention is now being given to reproductive health management ; but correlations between cow parity , milk yield , nutritional status , periparturient health , and fertility require clarification in korean dairy herds .
the objectives of this study were to determine the effect of parity on milk production , body condition change during early lactation , periparturient health , culling due to reproductive failure , and reproductive performance in korean dairy herds .
all herds contained 50 or more cows and received regular reproductive health checkups every 2 to 4 weeks from veterinarians at the college of veterinary medicine , chungbuk national university .
the cows were maintained in free - stall facilities and fed a total mixed ration , based on brewer 's grain , alfalfa hay , cotton seed , beet pulp , sweet sorghum , tall fescue , oat hay , and additives .
data were collected from 1,290 calvings in eight dairy herds from october 2000 to may 2005 .
data were collected on milk yield , body condition score , cow parity , calving condition , disease occurrence , culling due to reproductive failure , and reproductive status .
body condition was scored using standard procedures based on a scale of 1 to 5 , as described by edmonson et al . .
abnormal partus included ; dystocia ( veterinary - assisted calving or pulling with extreme force ) , caesarean section , twins , or stillbirth .
the postpartum reproductive and metabolic disorder definitions used in this study are similar to those used in previous studies
. retained placenta was defined as the retention of the fetal membrane for > 24 h .
metabolic disorders ( abomasal displacement , milk fever , or ketosis ) were diagnosed by clinical signs observed by a veterinarian and/or the farmer concerned within 4 weeks postpartum .
abomasal displacement was diagnosed by a pinging sound upon abdominal auscultation by a veterinarian , and all cases were corrected by surgery .
milk fever was diagnosed by the presence of the following clinical signs : weakness , cold skin , and a favorable response to calcium therapy .
ketosis was defined as the presence of the following clinical signs ; anorexia , depression , and an odor of acetone in breath .
endometritis was diagnosed at 4 weeks postpartum by examination by the corresponding author , by the presence of the following clinical signs ; cloudy discharge and an enlarged uterus observed by rectal examination with or without other clinical signs .
ovarian cysts were diagnosed from 4 to 16 weeks postpartum by repeated ultrasonographic examinations at 2 to 4 week intervals ( sonoace 600 with a 5.0 mhz linear - array transducer ; medison , korea ) .
ultrasonographic evaluations were based on ovarian structures of larger than 25 mm internal diameter with a wall less than 3 mm thick ( follicular cyst ) or with a wall greater than 3 mm thick ( luteal cyst ) in the absence of a normal corpus luteum .
cows diagnosed with ovarian follicular cysts beyond 8 weeks postpartum were treated with 100 g fertirelin acetate ( gnrh ; conceral , korea ) and cows diagnosed with luteal cysts were treated with 25 mg pgf2 ( lutalyse ; pharmacia & upjohn , belgium ) . the cows with endometritis were treated with one intrauterine infusion of 1500 mg oxytetracycline hydrochloride solution ( metrijet 15 ; intervet , u.k . ) or 2% povidone - iodine solution ( korea pharma , korea ) , and retreated if necessary . the voluntary waiting period from calving to first artificial insemination ( ai ) established for this study was 50 days .
the conception to ai ratio were determined per rectum 60 to 70 days after ai by both ultrasonographic observation and manual palpation .
reproductive performance data were collected for a minimum of 7 months postpartum or until pregnancy or culling .
parity in these herds was categorized as 1 , 2 , 3 , 4 , or 5 or higher .
body condition score changes versus parity from calving until months 5 of lactation were also compared by anova .
the occurrences of periparturient disorders and culling rate among the various parities were evaluated using the chi - square test or fishers ' exact test .
all herds contained 50 or more cows and received regular reproductive health checkups every 2 to 4 weeks from veterinarians at the college of veterinary medicine , chungbuk national university .
the cows were maintained in free - stall facilities and fed a total mixed ration , based on brewer 's grain , alfalfa hay , cotton seed , beet pulp , sweet sorghum , tall fescue , oat hay , and additives .
data were collected from 1,290 calvings in eight dairy herds from october 2000 to may 2005 .
data were collected on milk yield , body condition score , cow parity , calving condition , disease occurrence , culling due to reproductive failure , and reproductive status .
body condition was scored using standard procedures based on a scale of 1 to 5 , as described by edmonson et al . .
abnormal partus included ; dystocia ( veterinary - assisted calving or pulling with extreme force ) , caesarean section , twins , or stillbirth .
the postpartum reproductive and metabolic disorder definitions used in this study are similar to those used in previous studies .
retained placenta was defined as the retention of the fetal membrane for > 24 h .
metabolic disorders ( abomasal displacement , milk fever , or ketosis ) were diagnosed by clinical signs observed by a veterinarian and/or the farmer concerned within 4 weeks postpartum .
abomasal displacement was diagnosed by a pinging sound upon abdominal auscultation by a veterinarian , and all cases were corrected by surgery .
milk fever was diagnosed by the presence of the following clinical signs : weakness , cold skin , and a favorable response to calcium therapy .
ketosis was defined as the presence of the following clinical signs ; anorexia , depression , and an odor of acetone in breath .
endometritis was diagnosed at 4 weeks postpartum by examination by the corresponding author , by the presence of the following clinical signs ; cloudy discharge and an enlarged uterus observed by rectal examination with or without other clinical signs .
ovarian cysts were diagnosed from 4 to 16 weeks postpartum by repeated ultrasonographic examinations at 2 to 4 week intervals ( sonoace 600 with a 5.0 mhz linear - array transducer ; medison , korea ) .
ultrasonographic evaluations were based on ovarian structures of larger than 25 mm internal diameter with a wall less than 3 mm thick ( follicular cyst ) or with a wall greater than 3 mm thick ( luteal cyst ) in the absence of a normal corpus luteum .
cows diagnosed with ovarian follicular cysts beyond 8 weeks postpartum were treated with 100 g fertirelin acetate ( gnrh ; conceral , korea ) and cows diagnosed with luteal cysts were treated with 25 mg pgf2 ( lutalyse ; pharmacia & upjohn , belgium ) . the cows with endometritis were treated with one intrauterine infusion of 1500 mg oxytetracycline hydrochloride solution ( metrijet 15 ; intervet , u.k . ) or 2% povidone - iodine solution ( korea pharma , korea ) , and retreated if necessary . the voluntary waiting period from calving to first artificial insemination ( ai ) established for this study was 50 days .
the conception to ai ratio were determined per rectum 60 to 70 days after ai by both ultrasonographic observation and manual palpation .
reproductive performance data were collected for a minimum of 7 months postpartum or until pregnancy or culling .
parity in these herds was categorized as 1 , 2 , 3 , 4 , or 5 or higher .
body condition score changes versus parity from calving until months 5 of lactation were also compared by anova .
the occurrences of periparturient disorders and culling rate among the various parities were evaluated using the chi - square test or fishers ' exact test .
during the study period , the average percentages of cows with parities of 1 , 2 , 3 , 4 , or 5 or higher were 31.1 , 27.9 , 20.5 , 11.8 , and 8.7% , respectively .
mean 305 day milk yield increased ( p < 0.01 ) with increasing parity ( fig .
1 ) ; yields for parities of 1 , 2 , 3 , 4 , and 5 or higher were 8,431 , 9,774 , 10,191 , 10,812 , and 10,611 kg , respectively .
cows with parities of 3 , 4 , and 5 or higher lost more body condition ( p < 0.01 ) than those with a parity of 1 during the first month of lactation .
the recovery of body condition for cows with parities of 4 or 5 or higher was also more delayed than in cows with parities of 1 , 2 , or 3 until months 3 of lactation ( p < 0.01 ) , and body condition recoveries for cows with parities of 5 or higher was more continuously delayed ( p < 0.01 ) than in cows with a parity of 1 until month 5 of lactation .
the risks of retained placenta , metabolic disorder , and endometritis increased with parity ( p < 0.05 ) , whereas the risk of abnormal partus was highest for cows with a parity of 4 than in cows with other parities ( p < 0.01 ) .
the incidence of ovarian cysts was lower in cows with parity of 1 than in cows with other parities ( p < 0.01 ) .
moreover , the culling rate due to reproductive failure increased with parity ( p < 0.01 , fig .
however , the reproductive performance of cows was not significantly different for the various parities ( p > 0.05 , fig . 5 ) .
the data presented here demonstrate that advances in parity increase the risk of periparturient disorders and the incidence of culling due to reproductive failure in dairy herds .
we suggest that severe loss and delayed body condition recovery due to increased milk yield during the early lactation period are responsible . in the present study ,
mean 305 day milk yield increased with parity , which is consistent with previous reports .
body condition loss during early lactation , which reflects a negative energy balance , was found to be aggravated by parity , as has been reported by others .
the inverse correlation between body condition score and increased parity during early lactation is presumed to be related to milk yield , which is also consistent with previous results , and demonstrates that body condition scores , which reflect the amount of fat mobilized during early lactation , decrease as milk yield increases .
it has been reported that excessive lipid mobilization from adipose tissue , noted even in clinically normal cows during early lactation , may be linked to higher incidences of periparturient health disorders .
our finding of increased risks of a retained placenta and metabolic disorder in association with parity have been reported by others .
metabolic disorder is influenced by increased milk yield   and with a severe loss and delayed recovery of body condition during early lactation , and these are clearly and positively correlated with parity .
moreover , the correlation between an increased risk of endometritis and advancing parity , found in the present study , is in agreement with a previous study   but contradicts another .
this latter study found that the risk of endometritis is highest in first parity cows . on the other hand ,
an increased risk of endometritis may result from over - fattening and an increased rate of stillbirth in first parity cows .
however , our data do not support this hypothesis , and we regard our finding of an increased risk of a retained placenta in high parity animals as an important finding .
moreover , profound periparturient impairment of neutrophil function associated with advancing parity   might increase susceptibility to endometritis . the increased risk of abnormal partus in cows with a parity of 4 was mainly caused by an increased occurrence of twins in this parity group , although the reason for this higher incidence was not clarified .
in has been reported that the incidence of ovarian cysts is lower in cows with a parity of 1 than in other parities .
an increased incidence of ovarian cysts in animals with a higher parity may be related to high milk yield , and a clear relationship between milk yield and the incidence of ovarian cysts has been reported on a number of occasions . taken together , these results suggest that increased milk yield and concurrent severe body condition loss during early lactation elicit a severe energy deficit , which may be related to the occurrence of postpartum reproductive ( ovarian cysts ) and metabolic diseases . the major reason for involuntary culling is reproductive failure .
our finding that culling rates due to reproductive failure increase with advancing in parity is consistent with previous studies .
moreover , postpartum reproductive diseases can affect fertility and cause delayed conception , which may indirectly lead to culling .
likewise , in our study , the increased incidence of postpartum diseases associated with parity may have a reduced fertility and led to an increased need for culling . in the report of seegers et al .
, cows culled for reproductive disorders early in their lives ( parity 1 or 2 ) were high - yielding cows that were presumed to have had a negative energy balance during the early lactation period , a condition that is exacerbated in young and/or high - producing cows .
in fact , increased culling due to reproductive failure associated with parity increases might be attributed to a series of body stresses including high milk yield , concurrent exaggerated body condition loss , as well as to postpartum metabolic and reproductive diseases during the lactation period .
the mean intervals from calving to first service and conception for cows with different parities were no different .
however , the relationship between parity and fertility is difficult to determine because of the confounding effect of culling under farm conditions .
older cows are reportedly less likely to conceive , although we did not find this . our correlation between fertility and parity may be explained by our observation that culling rates increased with parity increases .
however , the reproductive performance of cows culled was not included in this study . in conclusion , this study shows that increases in parity increase milk yield , body condition loss during early lactation , and the risk of periparturient disorders and of culling due to reproductive failure in dairy herds .
 the objectives of this study were to determine the effects of parity on milk production , body condition change , periparturient health , and culling in korean dairy herds . 
 the data utilized included ; milk yield , body condition score , cow parity , calving condition , periparturient disorders , culling , and reproductive status , which were recorded from 1290 calvings in eight dairy herds . 
 the mean milk yield in cows over 305 days increased with increasing parity ( p < 0.01 ) . 
 cows with parities of 3 , 4 , and 5 or higher lost more body condition than those with a parity of 1 during month 1 of lactation ( p < 0.01 ) , and body condition recovery by cows with parities of 4 and 5 or higher was slower ( p < 0.01 ) than recovery by cows with parities of 1 , 2 , or 3 until month 3 of lactation 
 . the risk of retained placenta , metabolic disorder , and endometritis also increased with advancing parity ( p < 0.05 ) . 
 moreover , the incidence of ovarian cysts was lower in cows with a parity of one than in cows with greater parities ( p < 0.01 ) 
 . culling rate due to reproductive failure also increased with advancing parity ( p < 0.01 ) . 
 these results suggest that parity increases milk yield , body condition loss during early lactation , the risk of periparturient disorders , and culling due to reproductive failure in dairy herds . 
Introduction
Materials and Methods
Herds and data collection
Definitions of periparturient disorders
Evaluation of reproductive performance and culling
Data analysis
Results
Discussion