Applied Reproductive Physiology in ruminants Flashcards
Costs of Rearing replacement heifers
second largest expense in a dairy operation 20%
future of the diary operation
paradox: investment in feed, labour and capital for 22 to 24 months without receiving any realized benefits
on average costs 3.70 a day to feed
Goals of a Reproductive Program for Heifers
- decrease age at first calving with adequate body size and without compromising mammary development and future lactation performance
- has to be economically sound
- timed AI programs for heifers are economically attractive when estrous detection rate is ~70%
- achieve puberty and sexual maturity early
- achieve adequate BW, height, and frame size at calving
How to measure heifers growth
measure a representative subgroup of heifers in different age groups on the same day
plot weight or height by age- calculate parameters for the line
slope =ADG and AHG
longitudinal- measure each heifer or cohorts of heifers and follow at specific time points. analyst grouped data
Disadvantages of underfeeding heifers
heifers will reach puberty and calve later in life
- increase rearing costs
- increased farm inventory of heifers
- delayed milk income
- lifetime milk production is lower
lighter heifers produce less milk during first lactation
smaller frame heifers have increase risk for dystocia and limited capacity to compete for food and to ingest nutrients
reasons for slower growth rates
poor management
feeding forage of poor quality and quantity
- seasonal variation in forage
- stored forage
underfeeding grain supplements
inadequate bunk space
Prepubertal anestrus
not a major problem, unless the feeding program is poor or heifers are being inseminated before
Reproductive Programs for Heifers
importance of reproductive efficiency in heifers
- reduced rearing costs
- reduces variability in age at first calving
programs:
- natural breedings- not rec
- detection of spontaneous estrus
- detection of spontaneous and induced esters
- timed AI programs
Persistance of milk
more horizontal curve= more persistent milk
more vertical curve= less persistent milk
The Importance of Reproductive Efficiency to the Economy of the Dairy Farm
replacement heifers: reduces rearing costs, reduces variability in age at first calving
lactating cows:
- improves milk production - decreases the average days in milk of the herd - faster transition to a more productive stage in the following lactation
increases the number of replacement heifers
- allows greater genetic selection intensity
- allows selling heifers and cows for milk production
facilitates adequate culling policies
- culling of problem cows
- younger herd: better fertility, healthy, and genetic merit
To have good reproductive efficiency in a dairy herd, cows need… to be inseminated in a optimal time postpartum…
how to evaluate
- voluntary waiting period
- insemination rate
- DIM at 1st AI
risk factors
- an ovulation
- low detection of estrus
- management inconsistencies
solutions
- reduction of risk factors
- heat detection aids
- timed AI
- systematic breeding program
To have good reproductive efficiency in a dairy herd, cows need… to become pregnant in a optimal time post partum and maintain pregnancy
how to evaluate
- P/AI
- pregnancy losses
risk factors
- diseases
- low BCS
- anovulation
- nutritional deficiencies
- genetics
- heat stress
solutions
- reduction of risk factors
- genetic selection
- fertility treatments
Optimal insemination window
10 to 12 hours from estrus onset
Risk factors for low insemination rate- poor estrus detection
- high milk yield –> more blood flow to digestive tract so faster hormone metabolism
- bad flooring
- lameness
- low BCS
- heat stress
- inadequate training of employees
- inconsistent mangament
risk factors for low insemination rate- an ovulation
time to resume estrous cyclicality postpartum varies among cows
no estrous activity
directly related to energy balance postpartum
~20% of the cows reach the end of the VWP as anovular cows at 60DIM in Ontario dairy herds
Synchronization of the Estrous Cycle
prostaglandin injection to induce luteolysis
GnRH injection to induce ovulation
progesterone implant to prevent ovulation
Timed Artificial Insemination
objectives
- inseminate all cows in a prescheduled time with no need for estrous detection
- maximize insemination rate (100%) and consequently pregnancy rate
Ovsynch
GnRH– 7 days –> Pgf2alpha– 56 hours–> GnRH –16 hours–> AI
best results when the protocol is initiated in early diestrus (days 5 to 9 at GnRH 1)
Presynchronization
objective
- target cows to be in early diestrus at initiation of ovsynch
weekly based programs
day 1: PGF2alpha day 14: PGF2 alpha day 26: GnRH day 33: PGF2alpha day 35 pm: GnRH day 36 am: timed AI
Pregnancy diagnosis
28 to 34 days after AI
result = pregnant –> no action needed, recheck in 30 days
result non-pregnant–>
Actions: re=synchronization and timed AI
reinsemination at estrus
cull/dont breed
Considerations for Implementing timed AI programs
estrous detection rate in farm
- low EDR makes time AI more attractive
high EDR (>60%): impact of time AI become less evident - allows flexibility, but it won’t necessarily improve performance
timed AI might facilitate labour, but it also creates additional work and requires compliance
best response to timed AI
- management of first postpartum AI (all cows are eligible)
Fundamentals in Reproductive Management of Dairy Cows
work with groups of cows: pro-active management
focus is to increase the rate at which cows become pregnant past the voluntary waiting period
uses systemic breeding programs to minimize the missed”opportunities”
objective
- increase pregnancy rate
- reduce the interval and minimize the variability between the end of the voluntary waiting period and pregnancy in a consistent manner
21 day pregnancy rate
has been stuck around 15-17% for many years… lots of room for improvement
21-day insemination rate
this is what improves 21-day pregnancy rate currently 50%
pregnancy per AI
hasn’t changed in a long time… currently 35-38%
research is being done as to why it isn’t improving
embryo survival depends on
genetics of the cow genetics of the embryo low concentration of circulating steroids and IGF1 anovulation at initiation of synchronization heat stress and hyperthermia extensive loss of BCS low BCS at AI clinical diseases before and after AI
heat stress reduces pregnancy per AI
heat stress impairs oocyte quality and early embryonic development
incidence of clinical disease before first breeding (postpartum)
21% undiagnosed with uterine disease
25% diagnosed with non-uterine disease
40% diagnosed with at least one clinical disease
Clinical diseases postpartum
prevalent in dairy herds
long-lasting effects on production and reproduction traits
important pre-disposition factor for early and late pregnancy losses
clinical diseases postpartum Negative Effects on:
- oocyte quality
- fertilization of oocytes
- development to morula
- elongation of the conceptus
- survival of the developing fetus
Low BCS effect on pregnancy
cows with excessive loss of BCS (1 unit or more) during the early postpartum period have reduced pregnancy per AI
cows with low BCS at embryo transfer have reduced pregnancy per embryo transfer
Major Goal in Cow-calf operations
maximize quantity and quality of calves born each year
reproductive efficiency is key
ideally 1 calf per cow per year
Factors affecting reproductive efficiency in beef cows
postpartum anestrus suckling stimulus/presence of the calf age genetics nutrition plane of nutrition/body composition reproductive management animal handling and semen quality number and quality of bulls
factors affecting reproductive efficiency in beef heifers
prepubertal anestrous body weight age genetics nutrition plane of nutirtion/body composition reproductive management animal handling and semen quality number and quality of bulls
Breeding Season
pre-established period of the year in which cows and heifers should become pregnant
- calving occur within a short window of time
- facilitates management
- optimizes production efficiency
it should consider local environment and market conditions
- weather
- facilities and labour
- availability and price of feed
- demand for and market price of the final product
it should be short (ideally less than 3 months)
