Calf Birth and Age Determination Table


Guide B-210
Revised by Manny Encinias, John Wenzel, and Jason L. Turner
College of Agricultural, Consumer and Environmental Sciences, New Mexico State University


Authors: Respectively, Extension Beef Cattle Specialist, Extension Veterinarian, and Extension Horse Specialist, both of the Department of Extension Animal Sciences and Natural Resources, New Mexico State University. (Print Friendly PDF)

The table on the reverse side is designed to aid in keeping more complete and useful breeding, calving, and performance records in a beef cow herd. It can be used to determine the date when bulls should be removed from the breeding pasture, expected birth date of a calf, calving interval, and dates when calves should be weighed so that the weights can be standardized to 205- or 365-day weights.

The table itself has been reproduced from the booklet "Angus Breed Improvement," prepared by the American Angus Association. Note that it applies only to non-leap years; in leap years (2012, 2016, 2020, etc.), add one day for any date occurring after February 28.

How to Use the Table

Breeding Season. Assume bulls are turned out on May 1 (Day 121), and the breeding season is to extend for 75 days. Then, 121 + 75 = 196. So the bulls should be removed from the breeding pasture on July 15 (Day 196).

Expected Birth Date. Add 283 to the "day number" that the cow was bred. If date bred was June 5 (Day 156), the cow should calve about 283 days later, or March 15 (Day 439).

Calving Interval. If the calving interval in the herd averages more than 12 months, or 365 days, the management program should be reviewed. If a cow calves on March 15 (Day 74) and again on March 9 (Day 433) of the next year, her calving interval is 359 days.

205-Day Weight. Calves must be weighed between 160 and 250 days of age for correct adjustment to the 205-day weaning-age weight. Thus, the earliest date to weigh a calf born on March 15 (Day 74) is 160 days later, on August 22 (Day 234). November 20 (Day 324) is the last day that a March 15 calf can be weighed for a 205-day adjustment weight.

365-Day Weight. Yearlings must be weighed between 330 and 450 days of age for this adjustment. So, an animal born on March 15 (Day 74) must be weighed between February 8 (Day 404) and June 8 (Day 524) of the following year to determine the adjusted weight.

Julian Calender
Day of
Year #1
Day of
Year #2
Month Jan Feb Mar April May June July Aug Sept Oct Nov Dec Month Jan Feb Mar April May June July Aug Sept Oct Nov Dec
1 1 32 60 91 121 152 182 213 244 274 305 335 1 366 397 425 456 486 517 547 578 609 639 670 700
2 2 33 61 92 122 153 183 214 245 275 306 336 2 367 398 426 457 487 518 548 579 610 640 671 701
3 3 34 62 93 123 154 184 215 246 276 307 337 3 368 399 4274 58 488 519 549 580 611 641 672 702
4 4 35 63 94 124 155 185 216 247 277 308 338 4 369 400 428 459 489 520 550 581 612 642 673 703
5 5 36 64 95 125 156 186 217 248 278 309 339 5 370 401 429 460 490 521 551 582 613 643 674 704
 
6 6 37 65 96 126 157 187 218 249 279 310 340 6 371 402 430 461 491 522 552 583 614 644 675 705
7 7 38 66 97 127 158 188 219 250 280 311 341 7 373 403 431 462 492 523 553 584 615 645 676 706
8 8 39 67 98 128 159 189 220 251 281 312 342 8 373 404 432 463 493 524 554 585 616 646 677 707
9 9 40 68 99 129 160 190 221 252 282 313 343 9 374 405 433 464 494 525 555 586 617 647 678 708
10 10 41 69 100 130 161 191 222 253 283 314 344 10 375 406 434 465 495 526 556 587 618 648 679 709
 
11 11 42 70 101 131 162 192 223 254 284 315 345 11 376 407 435 466 496 557 557 588 619 649 680 710
12 12 43 71 102 132 163 193 224 255 285 316 346 12 377 408 436 467 497 528 558 589 620 650 681 711
13 13 44 72 103 133 164 194 225 256 286 317 347 13 378 409 437 468 498 529 559 590 621 651 682 712
14 14 45 73 104 134 165 195 226 257 287 318 348 14 379 410 438 469 499 530 560 591 622 652 683 713
15 15 46 74 105 135 166 196 227 258 288 319 349 15 380 411 439 470 500 531 561 592 623 653 684 714
 
16 16 47 75 106 136 167 197 228 259 289 320 350 16 381 412 440 471 501 532 562 593 624 654 685 715
17 17 48 76 107 137 168 198 229 260 290 321 351 17 382 413 441 472 502 533 563 594 625 655 686 716
18 18 49 77 108 138 169 199 230 261 291 322 352 18 383 414 442 473 503 534 564 595 626 656 687 717
19 19 50 78 109 139 170 200 231 262 292 323 353 19 384 415 443 474 504 535 565 596 627 657 688 718
20 20 51 79 110 140 171 201 232 263 293 324 354 20 385 416 444 475 505 536 566 597 628 658 689 719
 
21 21 52 80 111 141 172 202 233 264 294 325 355 21 386 417 445 476 506 537 567 598 629 659 690 720
22 22 53 81 112 142 173 203 234 265 295 326 356 22 387 418 446 477 507 538 568 599 630 660 691 721
23 23 54 82 113 143 174 204 235 266 296 327 357 23 388 419 447 478 508 539 569 600 631 661 692 722
24 24 55 83 114 144 175 205 236 267 297 328 358 24 389 420 448 479 509 540 570 601 632 662 693 723
25 25 56 84 115 145 176 206 237 268 298 329 359 25 390 421 449 480 510 541 571 602 633 663 694 724
 
26 26 57 85 116 146 177 207 238 269 299 330 360 26 391 422 450 481 511 541 572 603 634 664 695 725
27 27 58 86 117 147 178 208 239 270 300 331 361 27 392 423 451 482 512 543 573 604 635 665 696 726
28 28 59 87 118 148 179 209 240 271 301 332 362 28 393 424 452 483 513 544 574 605 636 666 697 727
29 29 88 119 149 180 210 241 272 302 333 363 29 394 453 484 514 545 575 606 637 667 698 728
30 30 89 120 150 181 211 242 273 303 334 364 30 395 454 485 515 546 576 607 638 668 699 729
 
31 31 90 151 212 243 304 365 31 396 455 516 577 608 669 730

Original authors: Larry Foster and Ron Parker, former Extension beef cattle specialists.


Photo of Manny Encinias


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Revised and electronically printed November 2011, Las Cruces, NM.