When should I turn the bull in for spring calves?

Short answer

About nine months — 283 days — before the first calf: bull in April 1 for calves from about January 9

Turn the bull in about nine months before you want the first calf (Oklahoma State); at 283 days, April 1 gives calves from about January 9 — UGA's calendar uses the same April 1 turnout for calves from January 10. Put him with the heifers a month earlier, and pull him after 45 days (Oklahoma State: 45 is better than 60, 60 better than 90). Feed cows 10–15% more for the last 30–45 days. A newborn calf below 100°F is hypothermic; it needs colostrum in its first 2–4 hours and about 10% of its body weight in the first day.

The arithmetic

Bull-in date = the first calf you want − 283 days. April 1 → about January 9; May 1 → about February 8.
Heifers a month ahead of the cows (UGA), so they calve first and have longer to rebreed.
Calving season = breeding season. 45 days of bull is 45 days of calving; take him out.
Colostrum = 10% of body weight in the first day (K-State) — about 2 quarts per feeding for an 80-lb calf, twice (Oklahoma State).

How much colostrum does a calf need — 10% at once, or 5–6% twice?

The two Plains extension services agree on the total and differ on the schedule.

K-State: 10% of body weight, or 0.5–1 gallon, within the first 2 hours — 4–6 hours if it has to come from a bottle or tube; 1.5 quarts is a good starting dose
Oklahoma State (Cow-Calf Corner): 5–6% of body weight within the first 4 hours, repeated at about 12 hours — roughly 2 quarts per feeding for an 80-lb calf
K-State: Replacer with at least 100 g IgG per dose; freeze collected colostrum in dated quart bags
Oklahoma State: Warm colostrum to 100–102°F before feeding

Five to six percent twice is ten to twelve percent in the first 12 hours — the same total as K-State's 10%, split because a cold or weak calf may not hold it all at once. The urgency is shared: absorption falls off fast after birth.

Get about 2 quarts into an 80-lb calf in its first few hours and another 2 by 12 hours. If it's cold, warm it first.

What changes your number

When to step in. Stage one over 8 hours; water sack showing 2 hours and she isn't trying; trying 30 minutes with no progress; quit for 15–20 minutes after progress; or anything other than two front feet and a head (K-State).
Body condition at calving. 5.5–6 for first-calf heifers, 5–5.5 for mature cows (K-State). Thin cows calve weaker calves and rebreed late.
Feeding time. Shift feeding to dusk or later a week before calving to move more calving into daylight (K-State).
Weather. Wet and below 50°F with wind is hard on a newborn, especially after a long birth (Oklahoma State). The cold-weather table on the cattle hay page shows what it does to the cow's feed.
After calving. A cow's nutrient needs rise by at least 50% after calving (UGA) — the hay pile has to cover that, too.
Tube feeders. Keep two, marked: one for healthy calves, one for sick ones only, and handle the healthy calves first (K-State).

A number we won't give you

A wind-chill line for newborn calves. Oklahoma State names wet weather below 50°F with wind as the danger; we did not find a published wind-chill threshold for calves and won't invent one.

Cold calf — numbers to have in the truck

Check	Number	Source
Normal newborn temperature	101.5–102.5°F	Oklahoma State
Needs help	below 101°F	Oklahoma State
Mildly hypothermic	below 100°F	Oklahoma State
Severe — organs cooling	below 94°F	Oklahoma State
Warm-water bath	about 100°F, raised gradually; stop external heat at 99°F	Oklahoma State
Colostrum temperature	100–102°F	Oklahoma State
First colostrum	within 2 hours (from the dam); 4–6 hours by bottle	K-State

Rectal temperature. Oklahoma State: calves that get colostrum within 2–4 hours of birth generally do much better for the rest of their lives.

Calving kit

Item	Why
OB chains and handles, calf puller	A malpresentation or a big calf
OB gloves and lube	Checking position
Betadine or Nolvasan	Non-irritant antiseptic
Flank rope	Laying a cow down
Old towels	Drying is the first warming
Cooler of warm water	Warm water in a cold barn
Two esophageal feeders, marked	Healthy calves and sick calves, never shared
Frozen colostrum in dated quart bags, or replacer (100 g IgG+)	A cow with none, or twins
Thermometer	Every slow calf

From K-State's calving checklist.

Run your own numbers

Pick the date you want the first calf and it dates bull-in for heifers and cows, bull-out, and the jobs before calving.

SpeciesFirst calf wanted onBreeding season (days)

313 days before
Bull in with the heifers — a month ahead of the cowsUGA
283 days before
Bull in with the cowsOklahoma State: about nine months before calving
238 days before
Bull out after a 45-day seasonOklahoma State: 45 days is best; UGA: 45–60
45 days before
Feed up 10–15% for the last 30–45 daysUGA
14 days before
Calving kit, tube feeders and pens checked; heavy heifers to a clean pasture you can seeK-State; UGA
7 days before
Move feeding to dusk to pull calving into daylightK-State
Day 0
First calfves due
45 days after
Last calves from the breeding season due

Gestation is an average; individual animals run a few days either side. Vaccine timing is the extension guidance — your vet’s plan for your herd comes first.

What calving season costs in feed

UGA puts the late-gestation increase at 10–15% for the last 30–45 days — about a pound of extra TDN a day — and the post-calving increase at 50% or more. On the cattle hay page's figure of about 30 lb of hay a day for a 1,200-lb cow, that is 3–4.5 lb more a day before calving and 15 lb or more after. Calve in January and that lands on the coldest weeks, when the cold rule adds 1% per degree of wind chill below 32°F on top.

Then stop planning from averages

The planner gives you the calendar. In Homestead Paradise you log each breeding and the app works out the due date and counts down to it, records the preg check, calving ease and birth weight, and works out adjusted weaning weights in the fall. The herd's feed and vet costs go on the same books. 14-day free trial, no card.

Start your 14-day trial — no card

Keep planning

How much hay do goats need for winter?How much hay do sheep need for winter?How much hay does a cow need for winter?How many bales of hay do I need for winter?What does it cost to feed livestock through winter, per head?How much water do livestock drink in winter?

Sources

Every figure on this page comes from a land-grant university extension service, a government agriculture or energy agency, or a breed registry — never from another blog.